hypothesis for mold growth

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Mold Bread Experiment

What makes mold grow.

We are going to perform a mold bread experiment to grow our own mold and find out whether mold does indeed grow faster at higher temperatures.

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In ten days you will be able to answer this important question and make a contribution to science!

But what is mold? What makes it grow?

What is Mold?

Mold is something that we often take for granted, as something that makes us have to throw the bread away or the cheese smell bad.

Mold is, in fact, a fascinating organism which has had many different uses over the years and our lives would not be the same without it.

Most of us know that food seems to become moldy more quickly in the summer than in the winter when it is colder. Food in refrigerators seems to keep longer than food left out in the sun. Is this true? Does temperature really affect the rate at which mold grows?

Important Note

Please note that some people are allergic to mold; ask your doctor or parents. If this is the case, do not pick the Mold Bread Experiment. Always wear gloves and a mask, wash your hands, and don’t eat or drink whilst you are performing this study.

Performing the Mold Bread Experiment

In the Mold Bread Experiment we are trying to prove that;

"Mold grows quicker at higher temperatures."( Hypothesis )

What You Need for the Mold Bread Experiment

• 15 slices of bread. Any sort will do but it is perfectly fine to use cheap white sliced bread as then you will know that all of the slices are a similar size, weight and thickness. You must make a note of the brand and use-by date so that anybody else wanting to repeat the Mold Bread Experiment can use the same type.
• 15 sealable sandwich bags
• 1 piece of film or clear plastic with a 10x10cm grid drawn onto it
• Clean knife
• Chopping board
• Sticky labels
• Mold Spores - if you can’t get these from your school don’t worry. There are mold spores all around us in the air which will eventually grow on the bread but your experiment will take longer.
• Using the sticky labels and the marker pen label the bags. Mark 5 bags as ‘A’, 5 as ‘B’ and 5 as ‘C’. You also need to label each set of bags 1 to 5.
• Cut the bread into 10 x 10 squares using the chopping board and knife.
• Inoculate the bread thoroughly with the mold solution. Try to coat each slice with a similar amount of the culture although this can be difficult.
• Put one slice of this bread into each bag and seal the bags tightly.
• Put the 5 ‘A’ bags into the freezer, the 5 ‘B’ bags into the refrigerator and the 5 ‘C’ bags somewhere safe in a warm room. Because the bags in the freezer and fridge will not be getting much light it is best to cover the ‘C’ bags to make sure that light is a constant.
• Every 24 hours, preferably at exactly the same time every day, using the plastic grid, count the number of square centimeters of mold on each slice of bread. If the mold covers more than half a square, count it as 1cm, if less than half a square, count as 0 cm. You must never open the bags.
• You should repeat these counting processes for 10 days or until there are significant measurable results .
• Keep a careful note of your results for each slice of bread for the entire duration of the experiment. You can even take pictures or draw the slices if you want to be really scientific!
• Average the results for sample types A, B and C.
• Once you have finished, throw out all of the bags without opening them.

Because each square of bread is 100 cm2, you can express your results as a percentage. For each of the bread types, A, B or C average the amount of mold grown over the ten days and write these figures into a table.

You can then plot this information onto a graph and begin to explore your results. You can plot the amount of mold on each bread sample and compare it to the number of days, like in the diagram below. This can be done with a sheet of graph paper and colored pens or on a computer.

Is the Graph Correct?

Could you replicate the graph below or is your graph different? We have done this, but will not give you our answer, so you can test for yourself!

Why are the Results Important?

The food industry spends millions of dollars every year on refrigeration and it is very important that they know what temperature they need to stop mold from growing. Moldy food must be thrown away and this costs restaurants and manufacturers a lot of money.

For companies using mold to make food or medicine they need to know at which temperature mold grows best. The faster the mold grows, the quicker they can sell their product and make money.

Further Experiments

Now that you have finished and obtained some results, maybe you want to see if other variables affect the rate at which mold grows. Maybe you could keep the temperature the same for all of the samples but use different types of bread.

You could try adding moisture to the slices or putting different amounts of sugar or lemon juice onto the slices. As long as you only vary one thing at a time, you can make some interesting studies about mold.

Temperature is not the only thing that affects the rate of mold growth so feel free to try and find out more about this interesting organism.

Facts About Mold

• Mold is not a plant but a fungus like mushrooms and toadstools. It grows on food and other organic matter, breaking it down into slime and extracting nutrients for growth.
• Alexander Fleming discovered that a common type of mold fungi kills germs. From this, he made a medicine called penicillin which has saved millions of lives over the last 80 years. Many other life-saving drugs are made from chemicals obtained from mold.
• Mold is one of nature’s cleaners. It breaks down dead organic material and recycles the nutrients back into the soil. It is essential in nearly every ecosystem in the world.
• We use molds for flavor in some foods such as blue cheese, soy sauce and Quorn (TM) .
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Martyn Shuttleworth (Nov 24, 2008). Mold Bread Experiment. Retrieved Sep 07, 2024 from Explorable.com: https://explorable.com/mold-bread-experiment

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Factors affecting the the growth of molds or yeast

Introduction: (initial observation).

Molds are varieties of multi-cellular organisms that grow on bread, fruits, cheese and almost any other dead organic matter.

Learning about the factors that affect the growth of mold and yeast can help us to control reproduction of these micro organisms.

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

What you will see in this project is just an example of information and experiments about growing mold and Yeast. You need to read this information and then come up with your own procedures. First you will decide which one you want to study on. Mold is an easy one, but you may select yeast as well. The next step is growing the organism that you select in order to make yourself familiar with what is involved. In your final step, you will repeat growth experiment at different conditions of light, moisture, and temperature. Finally, you will compare the results and draw a conclusion.

Information Gathering:

Find out about mold, yeast or other types of fungi, how they grow, and where they grow. Read books, magazines or ask professionals who might know in order to learn about different types of fungi. Keep track of where you got your information from.

Click here to see a sample project related to mold growth.

Mold if a fungi. Click here for a good source of information about fungi.

TRY GROWING YOUR OWN MOLDS IN A MOIST CHAMBER!!!

The material that supports the growth of a fungus is called its substrate. A commercially prepared medium like potato agar is one kind of substrate, but any organic material can be used.

The simplest method of growing molds is to put a substrate like bread in a moist chamber. The substrate provides nutrients, and the chamber maintains the high humidity that favors the growth of fungi. Placing a slice of bread, fruit or vegetable, or a leaf in a plastic sandwich bag is a simple way to use this method. The small plastic bag must have a tie, a fold-over top or another way of sealing it. Mold growth should be visible after 3 to 5 days. If you want to try this experiment, follow the directions below.

You will need the following items:

• Substrate material
• Sandwich bags with a tie, fold top or “zip lock”.
• A marker to label the bags.
• Damp, NOT WET, paper towels.

Making the moist chambers

• Label the bags with a number so you can tell them apart.
• Place a damp towel in each bag.
• Place a slice of bread or other substrate on top of the damp towel.
• Seal the bags.
• Record the substrate put in each bag.
• Place the bags in a warm area out of direct sunlight where they will not be disturbed.
• Check the bags each day. Fungal growth should be visible in 3 to 5 days. Fungi are fuzzy or hairy and may be green, white, black, yellow, etc. Bacterial colonies are shiny or slimy and may also be different colors.
• Record the number, color, and size of the fungal colonies. One very fast growing fungus, the Galloping Grey Ghost (Rhizopus stolonifer), may completely cover bread in just a couple of days.

Questions to help design experiments

• Does the amount of light affect the growth of mold?
• Does moisture affect the mold growth?
• Does temperature affect the mold growth?
• Are there differences in the numbers and kinds of fungi growing on different kinds of bread?
• Does preservative in some bread affect the numbers and kinds of molds?
• Are there differences in the numbers and kinds of fungi growing on bread compared to carrots?

TRY GROWING YOUR OWN YEAST !!!

The yeasts are one very important group of fungi. The common yeast used in baking bread grows very fast. You can complete an experiment in two days! The basic idea in this method is to measure the amount of carbon dioxide (CO2) released during the growth of yeast. The growth of the yeast stops when one of the nutrients required by the yeast is gone, or when the liquid gets too acid (low pH) and kills the yeast. If you want to try this experiment, follow the directions below.

• A teaspoon measure
• A permanent marker
• Active dry yeast (used in baking bread–do not use quick-rising varieties.) This yeast is available in jars if you are planning on doing a large experiment.
• Bottled soda pop or water in equal amounts. Different items contain different ounces per container. Shake each soda bottle and let the foam settle before opening, or open and allow to go flat overnight.
• Identical round, thin latex balloons–“water balloons” are slow to expand. Non-Mylar® “helium-quality” balloons give good results.

Directions for growing yeast

• Label each bottle with a number to keep track of what each one contains–control, treatment and contents, so that you can tell bottles containing the same solution (replicates) apart. Color is not a reliable means of identification–the caramel color used in cola is a carbohydrate and the yeast can eat it.
• Put a teaspoon of dried yeast in each bottle.
• Seal the bottles tightly and shake the bottle.
• Remove the lids and stretch a balloon over the mouth of each bottle. The balloon should fit very tightly so that the carbon dioxide does not leak into the air.
• Place each container in a warm area out of direct sunlight (top of refrigerator or clothes dryer) where they will not be disturbed.
• Record the diameters of the balloons, time since start of experiment, etc. for each bottle. One good method of measurement is to wrap a string around each bottle at its widest point, and then measure the length of the wrapped string against a yardstick. Record any other things you see happen. Did the color change? Did one balloon have a hole in it?
• Calculate the average diameter of the balloons in each treatment and the controls. The average is calculated by adding all the diameters of all the balloons in a treatment then dividing by the number of balloons in the treatment.
• Compare the results (average balloon diameters) of the experiment.
• A graph of the averages might help show your results.
• Is the average of the treatments larger than the average of the controls?
• Is the average of one treatment larger than the averages of the other treatments?
• Is carbonated water a better control than non-carbonated water in experiments with different kinds of soda pop?
• Is the amount of sugar used in a bottle related to the amount of carbon dioxide released into the balloon? Hint: graph sugar concentration versus average balloon size.

An Alternative to the Balloon Method for Measuring Yeast Respiration

The apparatus shown in the picture permits more accurate measurement of yeast respiration than the balloon approach. The carbon dioxide respired by the yeast is trapped in an upside down graduated cylinder. The milliliters marked on the graduated cylinder let you read directly the amount of carbon dioxide trapped.

You will need:

• graduated cylinder (100 ml shown).
• beaker or bowl.
• rubber or plastic tubing.
• one hole rubber stopper. A number 3 stopper fits most 1 liter plastic soda bottles.
• short glass or plastic tube. A medicine dropper or piece of a 1 ml plastic pipette might work. The tube should not touch the liquid culture in the flask or bottle.
• Erlenmeyer flask or soda bottle (500 ml flask shown).

Directions for assembly:

• Buy one-hole rubber stoppers that fit your bottles or flasks. Your teacher may be able to help or hobby stores that sell chemistry sets often have the supplies you will need.
• Insert a short piece of glass or plastic tubing in the hole in the stopper. It will be easier to insert the tube if you put salad oil on the outside of the tube. BE CAREFUL. If you break the glass tube you may cut yourself.
• Measure and cut a piece of rubber tubing long enough to reach from the flask to the lower part of the graduated cylinder.
• Slide one end of the rubber tubing over the tube in the rubber stopper.
• Fill the beaker or bowl with water.
• Fill the graduated cylinder all the way to the top with water.
• Cover the top of the graduated cylinder with your hand and quickly turn it over and put it in the beaker filled with water.
• Remove your hand. There should not be any air in the graduated cylinder. If there is a small amount of air, record the amount (ml). You will need to subtract this amount from the total in the cylinder when you take respiration measurements.
• Fill the flask or bottle with your liquid yeast culture.
• Insert stopper in the flask or bottle.
• Insert the end of the rubber tube in the graduated cylinder. Do not lift the end of the graduated cylinder out of the bowl or it will fill with air.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Temperature, moisture and light are among the factors that may be studied for their effect on the growth of mold, yeast, or any other fungi.

These are samples of how you may define a question or purpose for your project.

The purpose of this project is to identify the effect of light on the growth of mold.

Note that instead of light you may choose other factor and modify your experiments accordingly. You can also substitute mold with yeast. This is another example:

The purpose of this project is to find out “How does the type of substrate affect the growth of yeast?”.

Substrate is a combination of food and growth media. Substrates such as water, sugar water, starch solution, flat soda,.. may be compared.

You may be much more specific and have a purpose like this:

Does yeast need air to grow?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

This is a sample of how you define the variables:

• Independent variable (also known as manipulated variable) is light.
• Dependent variable (also known as responding variable) is the mold growth.
• Controlled variables are temperature, substrate type (type of bread), moisture.
• Constants are all other experiment conditions such as the source of bread, type and size of the plastic bag.

You may want to study other factors (Independent variables) as well. Just make sure that the independent variables must be tested ONE at a time.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample of hypothesis:

My hypothesis is that molds grow best in a dark environment. Possibly light or certain radiations in the light spectrum can slow down or prevent mold growth.

This hypothesis is based on my personal observation on where mold is usually found at home.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

For example, in one experiment you may study the effect of light on growing mold. You may take three pieces of bread in three identical plastic bags and keep one of them at normal light to be your control and place two others, one in a dark place, and the other exposed to more than normal light. For a more reliable result you may use more samples. For example you may place 5 samples in a dark place, 5 samples in normal room light and 5 samples under a strong light source such as fluorescent light.

About Mold Experiment

As you know, we keep food in refrigerators so it will last longer. But still, sometimes you open a bag of bread or a jar of spaghetti sauce and what do you find? Mold!!

Ever wonder exactly what mold is? And how did it get there? And why sometimes it’s green and other times black or white? Did you know mold is a fungus and is alive and growing?

In this experiment, you’ll find out all about those colorful, fuzzy fungi by growing your own crop. Print out these pages and follow the directions to do this experiment at home. When you’re done, try answering the questions below.

Note: This is a long-term activity. It will take several days for the mold to grow. The first day should take you about 30 minutes to one hour to prepare everything. For safety reasons, don’t eat or drink while doing this experiment. And don’t taste or eat any of the materials used in this activity.

You’ll Need:

• 3 eye droppers
• small cup filled with 4 teaspoons or 20 mL of sugar water (see directions for preparing sugar water below)
• small cup filled with 4 teaspoons or 20 mL lemon juice
• small cup filled with 4 teaspoons or 20 mL tap water
• 4 slices of plain white bread*
• 4 slices of assorted bread, such as wheat, rye, sourdough, etc.*
• 8 resealable plastic sandwich bags
• masking tape

*It’s best if you use newly bought, fresh bread to make this experiment as accurate as possible.

Preparing sugar water

Note: Young people who don’t have experience operating a stove or microwave oven should get help and supervision from an adult. Parents or supervisors of young children may consider doing this step themselves.

Microwave: Stir 1/4 cup of sugar into 1/4 cup of water in a microwave-safe container and heat at one-minute intervals until sugar dissolves. Water will not need to reach boiling. Use potholders or oven mitts to handle container. Allow the mixture to cool for about five minutes before using.

Stovetop: Stir 1/4 cup of sugar into 1/4 cup of water in a small saucepan. Heat over medium heat until the sugar is dissolved. Use potholders to handle hot saucepan. Allow the mixture to cool for about five minutes before using.

What To Do:

1. Using masking tape and marker, make labels for four sandwich bags. Label the first bag “Dry White Bread.” Label the second “Water on White Bread,” the third “Lemon Juice on White Bread,” and the fourth “Sugar Water on White Bread.”

2. Wash your hands. Place a slice of white bread in the bag labeled “Dry White Bread” and seal the bag. Using one eye dropper, sprinkle 20 drops of tap water on another slice of white bread. (Don’t overdo it; the bread should be moist, not wet. If your bread is dripping, you’ve definitely done way too much. Throw away that slice and try again.) Place the moist bread in the bag marked “Water on White Bread” and seal the bag. Using a different eye dropper, sprinkle 20 drops of lemon juice on another slice of white bread and put it in the bag marked “Lemon Juice on White Bread” and seal the bag. Using your third eye dropper, sprinkle 20 drops of sugar water on the last slice of white bread and place it in the bag labeled “Sugar Water on White Bread” and seal. Try to keep your fingers off moist spots when handling each slice of bread.

3. Repeat steps 1 and 2, but this time use a different kind of bread in the remaining four bags. Your labels should note what kind of bread you’re using. Wash your hands when you’re done.

4. Make sure all of your bags are tightly sealed. Place all eight bags in a dark, warm place (about 86 degrees Fahrenheit, 30 degrees Celsius). Check with your parents or supervisor about where to store the bags. Check the bags each day for two weeks and record the results in a notebook. You may wish to draw or take pictures of the bread slices. Don’t open the bags!

5. Make a graph recording the total growth of mold on each of the four white bread slices at the end of two weeks (see sample graph on right). Make a similar graph for the other four bread slices. Compare the results. At the end of the two weeks, throw out all the bags unopened.

• From this activity can you tell what helps mold to grow best?
• Does it matter what kind of bread you use?
• What causes the different colors you see?
• What would happen if you left the bags in a well-lit place instead of a dark place?
• What would happen if you changed the temperature?

Answer 1: Unless you used bread that had been sitting out for many days, you probably didn’t get much or any mold growth on the dry bread. Clearly, water is important for the growth of mold. The mold grew best on bread sprinkled with sugar water because the sugar serves as food for the fungi. The more food that’s available, the more fungi cells can grow. The mold also grew pretty well on the bread with plain tap water because the fungi could use the sugar and starch in the bread as food. The mold didn’t grow as well on the bread sprinkled with lemon juice because lemon juice is acidic. Acids hinder the growth of many common fungi and bacteria. Answer 2: Molds grow better on some kinds of breads than others depending on the ingredients used and how the bread was made. Some breads are dry and some are moist. The amount of the sugar in different breads varies; some have sugar, honey or molasses added. Some breads are even acidic, such as sourdough. Some may have fruit or nuts or other ingredients added. Many commercial breads are made with preservatives that hinder the growth of molds and bacteria to prevent or delay spoilage. Bread baked fresh in a bakery that doesn’t use preservatives will more likely become moldy faster. All of these factors can influence how much mold will grow on a particular kind of bread.

Answer 3: Many of the colors you see on the moldy bread are due to the spores the fungi have produced. Molds reproduce by making spores at the end of stalks that rises above the surface of the bread, giving molds a fuzzy appearance. Spores are like seeds—they spread molds to new places so that they can continue to grow. Spores are usually colorful. Some fungi, such as Rhizopus nigricans (rye-zoh-puss neye-grih-cans) and Aspergillus niger (As-per-jill-us neye-jer), make black spores. Neurospora crassa (new-rah-spore-ah crah-sah) produces spores that appear pink. And the Penicillium (pen-ih-sill-ee-um) molds, the molds that make penicillin, are blue-green.

Some of the colors on your bread may be the result of growing colonies of bacteria, which also sometimes grow on old food. For example, a bacterium called Serratia marcescens (ser-ay-shuh mar-seh-sens) forms reddish colonies. You can tell bacteria colonies apart from molds because bacteria colonies appear smooth while molds look fuzzy.

Answer 4: Molds grow best in the dark, so not as much mold would be present on bread slices kept in a well-lit place.

Answer 5: Most fungi grow best around room temperature. But they can grow at a range of temperatures from cold (like in a refrigerator) to quite warm (body temperature). At temperatures colder or warmer than their favorite temperature, they usually do not grow as rapidly. If the temperature is too cold or too hot, they will not grow at all, and may even be killed.

Yeast growth experiment

As you probably know from eating numerous meals, all breads are not the same. Tortillas and pitas are flat and dense, while loaves of sandwich bread and dinner rolls are puffy and lighter. In fact, if you look closely at a piece of sandwich bread, you can see a honeycomb texture in it where bubbles formed and burst. Why these differences? Aren’t all breads made of the same basic ingredients? What made those bubbles?

The differences are caused by a microbe called yeast, pictured here. Yeast is a kind of fungus. If you open up a package of baker’s yeast bought from the supermarket and sprinkle some out, you’ll see tiny brownish grains.

These are clumps of dehydrated yeast cells (dehydrated means most of the water has been removed). Let them sit there for a while and watch them and you’ll soon get bored. They don’t exactly do much, do they? But put them in bread dough and after a while you can definitely see that they must be doing something. But what exactly are they doing?

You’ll find out in this activity in which you’ll make your own bread dough.

Note: This activity can be done within one hour, though you could stretch it over a few hours if you wish, depending on how many different sweeteners you want to try.

• 2 cups of flour (plus a little extra)
• 4 medium-sized bowls
• 2 packages of rapid-rise yeast
• access to warm water
• 6 teaspoons of sugar
• a sweetener besides sugar such as honey or artificial sweetener
• 24 clear drinking straws (must be clear)
• 24 clothespins
• measuring spoons
• ¼ cup measuring cup
• metric ruler
• permanent marking pen
• notebook and pen or pencil
• clock, watch or timer

1. Using the ruler, measure the point 3 centimeters from one end of each straw and mark that point with a line using the permanent marker.

2. Put ¼ cup of flour into each of your bowls. Mark the first bowl as the “Control.” Mark the others as 1, 2, and 3. (Just imagine that the dough in the illustration below is in four separate bowls.)

3. Measure 1 teaspoon of sugar and add it to the flour in the bowl marked 1. Put 2 teaspoons of sugar into bowl 2. Put 3 teaspoons of sugar into bowl 3.

4. Pour ¼ of a package of yeast (or ¼ teaspoon) into each of the four bowls. Using the spoon, stir together the ingredients in each bowl starting with the Control bowl.

5. Fill a cup with warm water from your faucet. The water should be warm, not hot and steaming. Dust your hands with a little flour. Carefully add the water to the Control bowl about a teaspoonful at a time and begin to knead the mixture. Your dough should eventually feel kind

of like Play-Doh—it should be damp, not wet. It’ll be sticky at first, but should eventually reach a point where it’s just damp enough that it no longer really sticks to the bowl or your hands. If it’s too sticky still, add a little bit more flour. Form the dough into a ball.

6. Repeat step 5 with each of the remaining bowls, working as quickly as you can. (If you have friends or classmates or parents helping out, each person should take a bowl and everyone should do step 5 at the same time.)

7. Working quickly, push three straws into the Control dough until the dough inside the straw reaches the 3-centimeter mark. Lay these straws by the Control bowl. Repeat this step with each of the remaining bowls.

Be sure to keep the straws beside the right bowls and don’t mix them up. (Again, if you’ve got more people working with you on this activity, each person should take a ball of dough and everyone should do this step all at the same time.)

8. Now pinch the bottoms of each of your Control dough straws, pushing the dough up from the bottom enough to clip a clothespin to the end of each straw. Mark the new height of the dough on each straw. Stand the straws upright using the clothespins as bases. Do the same with the rest of the straws. Label the batches of straws as Control, 1, 2 and 3.

9. Mark the time on your clock or watch or set your timer for 10 minutes. Wait 10 minutes. Then measure and mark the heights of the dough in each straw and record these heights and the time in your notebook. Repeat this step 10 minutes later. Repeat after another 10 minutes has passed.

10. During the 10-minute intervals while waiting for the dough in the straws to do its thing, discard your first batches of dough from each bowl and wash the bowls out. Dry them thoroughly. Be sure to keep an eye on the clock while you’re doing this so that you don’t miss the 10-minute deadline to check and measure your straws.

11. Repeat the dough making process only this time use a different kind of sweetener than sugar. Repeat the steps of filling and marking the straws. Label the new batch of straws and set them away from your first batch. Repeat the process of measuring the dough height in the straws at 10-minute intervals and recording the results in your notebook. Be sure to record the heights of this new batch of straws separately from the first batch.

12. Graph your results. First, calculate the average final height for each set of three straws in your first batch. Make a bar graph showing these average heights with the number of teaspoons of sugar (0, 1, 2, 3) on the horizontal axis and the height in centimeters on the vertical axis. Make a similar bar graph for your second batch of straws. See the sample graph on the right.

13. Throw away all the straws when you’re done. You might want to save the clothespins for another project in the future. Discard the dough in the bowls and wash them out. Clean up any spilled flour, sugar or yeast.

• In the first batch of straws you made, which straws showed the greatest change in dough height? Why?
• Can you guess what effect the sugar had and why?
• Did the Control dough rise at all or not? Why or why not?
• Did your dough made using a different sweetener besides sugar show the same results?

Answer 1: The straws containing dough from bowl 3 showed the highest rising. Since everything—the amount of flour, the amount of yeast, the temperature of the water—stayed the same except for the amount of sugar, you have probably already rightly guessed that the height of the dough rising is connected to the larger amount of sugar in this dough. Why is that? See the next question.

Answer 2: You will notice that the dough from the other bowls also rose some in their straws, the height connected to how much sugar was in the flour. The more sugar, the higher the dough rose. What can you figure out from this? Well, you’ve already read that yeast makes bread rise and become puffy instead of flat and this has something to do with yeast activity. What makes living things active? Food energy. The sugar is food for the yeast cells. The more sugar there is, the more active the yeast cells are.

Yeast cells chow down on the sugar molecules, breaking them apart in a chemical reaction and turning them into simpler elements and compounds including carbon dioxide. Carbon dioxide is a gas. Bubbles of carbon dioxide released by the yeast get trapped in the dough as bubbles. As more and more of these bubbles build up, the dough puffs up or rises. When the dough is put in the oven and baked, the carbon dioxide vaporizes in the heat, leaving spaces where the bubbles once and giving bread its honeycomb texture.

Answer 3: You probably saw some rising happen in the straws containing Control dough. This is because flour is a starch. Starches contain glucose, a form of sugar (this is why a saltine cracker tastes a little sweet if you let it sit on your tongue for a while; the enzymes in your saliva break the cracker starch down into glucose and other simpler molecules). So even though you didn’t add any sugar to the Control dough, it already contained some for the yeast to much on. However, because the amount of sugar in this dough was much less than in the others, less carbon dioxide could be made by the yeast in this batch and the dough couldn’t rise as much in comparison.

Answer 4: Different sweeteners will have similar or lesser effects on dough rising as sugar. You could try this experiment with as many different types of sweetening agents as you want to compare the results. Then you could do some research on the types of sugars in these different sweeteners to determine which ones work best as food for yeast.

Stop the Mold: A Bread Mold Study

This experiment examined how alcohol , pickle juice and mercurochrome affect mold growth. Mercurochrome and ethanol were selected because each stops wounds from infection. Pickle juice, a weak acid, was chosen to examine whether decreasing pH would inhibit mold growth. Method: Mold was grown on bread allowing enough growth so that mold type could determined. The most common mold growing was used to inoculate other four slices of bread. Three drops of mercurochrome, pickle juice, alcohol were each added to a slice, leaving the fourth slice as a control. Mold growth was recorded daily. Results: Pink, green, yellow and black molds grew on the bread. The green mold was used for this study. None of the agents tested totally inhibited mold growth although pickle juice worked the better than the other agents.

The main types of mold inhibitors are (1) individual or combinations of organic acids (for example, propionic, sorbic, benzoic, and acetic acids), (2) salts of organic acids (for example, calcium propionate and potassium sorbate), and (3) copper sulfate. Solid or liquid forms work equally well if the inhibitor is evenly dispersed through the feed. Generally, the acid form of a mold inhibitor is more active than its corresponding salt.

Any other chemical substance may also be tested for its effect on mold.

INTRODUCTION

To experiment with fungi, mycologists often need to grow them. Simply allowing bread to become moldy is not an experiment. An experiment is the test of an idea. Often, this idea is expressed in the form of the question: what? What if…? What happens when…? What kind of effect…? Experiments are designed to use the methods and materials that will give the most complete and accurate answer to an inquiry.

DESIGNING EXPERIMENTS

Fungi break down and absorb organic material for their nourishment, so any experiment must first provide them with food. Oxygen and moisture are also necessary. A material for the growth of fungi for experiments is called a medium.

Most commercially prepared media for growing fungi are extracts of plant materials like potatoes. A medium that is specially prepared to contain only the exact nutrients required by one species of fungus is called a “minimal medium”.

The choice of growth medium depends on the question that is being asked. If the question is “What kinds of fungi grow naturally on bread?” the choice of medium is simple. You could just put a slice of bread in a plastic bag, close it to retain moisture and await mold growth.

However, observing only one slice of bread would not make an effective experiment. Your chosen slice may not have any mold spores on it, or contain spores of all the species present in the loaf. It might be too dry to allow growth. You would have to use a number of bags to account for all reasonably possible growth failures and successes. The slices of bread would be replicates. Replicates allow the treatment to be repeated often enough to allow you to determine if the results are significant or the product of random chance..

You will also need to decide how to record your results. Do you identify each species of mold by its scientific name, or do you just describe them (fluffy red colonies, white fuzzy spots, blue-green velvet, etc.?)

A more complicated question requires the design of a more complicated experiment. At first glance, “What effect does the preservative in some breads have on mold growth?” seems as if it could be answered with a loaf of bread and some plastic bags, like the first experiment. However, the best experiment on the effect of a preservative on mold growth would use two loaves of bread. These loaves would be identical in preparation and ingredients, except for the presence or absence of the preservative. The bread without the preservative would be the control and the bread containing the preservative would be the treatment. Replication of both treatment and control gives the experimenter a way to understand the effect of substance by showing what happens when it is both present and absent.

Materials and Equipment:

Can be extracted from experiment design.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

No calculation is required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find some books and publications related to mold or fungus. Following are some online resources.

About Mold: http://www.e-tulsa.net/mold1.htm l

• Mildew Diseases
• Fungi of California
• Fungi of Sierra Nevada
• Tayside fungi

It is always important for students, parents and teachers to know a good source for science related equipment and supplies they need for their science activities. Please note that many online stores for science supplies are managed by MiniScience.

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Science Project

Science Project Ideas

Bread Mold Experiment

This biology experiment requires you to gather some background information before starting with the research. Once you know what the organisms called molds are, understanding the activity would be easy.

How to Do Mold Bread Experiment

A piece of bread kept under moisture and high temperature develops mold on its surface.

Materials Needed

• Slice of bread
• Plastic zipper bag
• Masking tape
• Camera (optional)
• Sprinkle water on the slice of bread.
• Put the bread in the plastic bag and zip it.
• Use the tape to secure it further.
• Write today’s date on the tape with the marker.
• Leave the bag undisturbed for 7 days in a warm place outside the house.
• Track the growth of the mold by checking the sample every day. Collect data in the notebook on the size and color of the colony. You can also take a photograph of the bread each day.
• In the end, throw away the bag with the moldy bread without consumption or inhalation near it.

You Can Also Try Out

• Instead of just 1 slice, take 3 slices of bread and mark them as A, B and C with the marker on the masking tape. Repeat the process by placing one in the refrigerator, one in a dark room and the last one in a sunny place. Observe and analyze the rate of mold growth under the different conditions of temperature and light.
• Check the results by keeping one of the variables like temperature constant for the 3 samples mentioned above but altering the type of bread in the different samples.
• Instead of adding moisture to the 3 slices as indicated in the steps above add different amounts of lemon juice or sugar to the slices. How does that affect the molding on the bread? What happens if you add salt?

For accurate measurements, you can take the help of a plastic grid to check how many squares or cm of it gets covered by the mold. While creating the lab report for your science experiment you can plot that data along the Y-axis and the no. of days along the X-axis on a graph paper.

Mold on Bread Project Video

What is happening a conclusion.

Mold is a fungus that best grows in dark, moist and warm conditions. It feeds on organic matter like bread while decomposing the same. Hence it is harmful to consume the moldy bread or even inhale the smell as mold spores could enter the body in that way. Adding salt inhibits the development whereas sugar enhances the method. Types of bread with high moisture content like rye, oat, Boston and other dark breads mold faster than the drier and denser varieties.

Some Interesting Facts

Many food industries depend on molds to produce food materials like soy sauce, country cured ham, certain types of cheese, etc. They need to know the favorable conditions for fast culture. On the other hand, there are other food industries that take measures to preserve the produce from molds. They utilize the knowledge of the unfavorable situations of infestation.

If you are planning to demonstrate molds growing on bread at a science fair, it is best to perform the experiment beforehand and exhibit the resulting samples for all to see with due explanation of the method adopted.

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MOLD GROWTH ON BREAD AND FRUIT

LEARNING OBJECTIVES

Differentiate between fungi and bacteria.

Perform basic mycological culturing.

Identify common household molds based on their macroscopic characteristics.

MCCCD OFFICIAL COURSE COMPETENCIES

Identify structural characteristics of the major groups of microorganism.

Compare and contrast prokaryotic cell and eukaryotic cells.

Compare and contrast the physiology and biochemistry of the various groups of microorganisms.

Apply various laboratory techniques to identify types of microorganisms.

Utilize aseptic technique for safe handling of microorganisms.

You want to grow mold, so you need bread that does not contain preservatives (natural or artificial), Please go the bakery section of the grocery store and look at the ingredients of bread they baked. Find bread that does not contain ascorbic, citric acid, or lactic acid and purchase that. Bread from the bread aisle will contain artificial or natural preservatives and therefore cannot be used in this experiment.

PHOTO REQUIREMENTS

Take a photo with your photo ID during the lab exercises when you see this icon.

Paste these photos into the Mold Growth on Bread and Fruit Questions Document.

introduction

Mycology is the study of fungus. Fungi can grow in a wide diversity of environments, but most species require moisture. Fungi grow slower than bacteria, at a lower temperature, and lower pH than most bacteria prefer. Most fungi are unable to ingest food and must absorb nutrients from their surrounding environment. For this reason, fungi must grow directly on or in their nutrient source. Fungi secrete enzymes into their surroundings to help break down their food source and facilitate the absorption process. Fungi are eukaryotic organisms which grow as either unicellular yeast or multicellular mold.

Mold plays an important role in the environment by breaking down and digesting dead organic material. Mold reproduces asexually by producing microscopic spores, similar to seeds produced by plants. Mold spores are ubiquitous; they are found everywhere both indoors and outdoors. Mold spores can easily float through the air and can be carried great distances. The number of mold spores suspended in indoor and outdoor air fluctuates from season to season, day to day, even hour to hour. If mold spores land in a suitable growth environment, they will germinate to produce new mold.

Mold produce multicellular filaments called hyphae.  Hyphal filaments intertwined into a mass, known as mycelia, can be seen macroscopically as fuzzy or hairy colorful growth. Mold absorb food through their extensive network of mycelia. There are three common household molds Rhizopus (white), Aspergillus (black) and Penicillium (green) you are likely to grow. In this experiment, you will determine which factors encourage mold growth on pieces of bread and apples.

Read all instructions carefully before you start the experiment.

EXPERIMENT VIDEO GUIDE

1. Use the measuring cup to measure and add 1/4 cup or 4 ounces of water to a saucepan or microwavable bowl and mix in 1/2 cup of sugar.

2. Gently heat the water-sugar mixture on the stove or in the microwave, stirring occasionally until all of the sugar is dissolved. Use caution when removing the solution from the microwave/stove as it will be hot. Allow the solution to cool. The cooled sugar-water solution will be a little thick, like syrup.

3. Use the permanent marker or grease pencil to label the plastic bags with the following titles: “Bright, Control,” “Bright, Water,” “Bright, Sugar,” “Bright, Lemon or Lime,” “Dark, Control,” “Dark, Water,” “Dark, Sugar,” and “Dark, Lemon or Lime”.

4. Cut the 6 slices of bread into 24 pieces total (4 pieces from each slice).

5. Cut the apple into 24 slices.

6. Place 3 pieces of bread and 3 slices of apple into each plastic bag.

7. Add 1 teaspoon water to the two bags labeled  “Bright, Water” and “Dark, Water”; add 1 teaspoon of the cooled sugar-water solution to the two bags labeled “Bright, Sugar” and “Dark, Sugar”; add 1 teaspoon of lemon or lime juice to the two bags labeled “Bright, Lemon or Lime” and “Dark, Lemon or Lime”. Do not add anything to the bags two labeled Control.

9. Find a well-lit, warm location (e.g. a windowsill or under a lamp) in which to place the 4 bags labeled “Bright”.

10. Find a dark, warm location (e.g. a warm closet) in which to place the 4 bags labeled “Dark”.

11. Examine the bags every day for 14 days and look for mold formation on the bread and apple pieces. Record the day (1-14) that mold growth was observed in the data table in the Mold Growth on Bread and Fruit Questions document. If no mold growth was observed in 14 days, record “no growth”. For example, if mold was first observed on the bread in the “Dark, Water” bag on day 3, record 3 in the data table. If no mold growth was observed in the “Control, Dark” bag after observing the bag every day for 14 days, record “no growth” in the data table. On day 14 record the number of pieces of apple (0-3) and the number of pieces of bread (0-3) in each bag that have mold growth in the data table.

AFTER 14 DAY INCUBATION WITH DAILY DATA COLLECTION

2. Do not open the bags when you are finished with the experiment. This will disperse mold spores and contaminate your work area. Dispose of the sealed bags in the trash and remove the trash bag from your living area.

DISCOVERIES IN MICROBIOLOGY

In 1950, American chemists Elizabeth Hazen and Fuller Brown discovered the antifungal drug nystatin. Hazen (in New York City) cultured hundreds of soil samples from around the world and tested them in vitro for activity against two fungi ( Candida albicans  and  Cryptococcus neoformans) . If the culture killed the two test fungi, she would mail the culture in a mason jar to Brown (in Albany New York).  Brown isolated the active agent in the culture and would send it back to Hazen. Hazen would then test it again against the two test fungi. If the active agent from the culture killed the two test fungi, its toxicity was evaluated in animals. Nearly all the agents that killed the test fungi turned out to be highly toxic in animals. Hazen and Brown tested hundreds of soil samples from around the world. The one successful culture was found in soil from the garden of a friend of Hazen. The culture contained an active agent they named nystatin (for New York State).  Nystatin has been used for years as an effective treatment for fungal infections of the skin, mouth, vagina, and intestinal tract.

Hands On Microbiology Copyright © 2022 by Jill Raymond. All Rights Reserved.

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Science Struck

A Simple Experiment to Grow and Study Bread Mold

Bread mold experiment is a fun science project, where one can observe the growth of a live organism on household bread! Here is a detailed guide that will help you in conducting this experiment.

Like it? Share it!

Many people tend to find mold growing on bread disgusting. But, did you know that mold is also one of nature’s cleansers , that breaks down dead organic materials and recycles these nutrients back to the soil, which makes it essential for the ecosystem?

Mold is a type of fungi, which grows on any plant or animal material. Mushrooms and toadstools are a type of fungi. Mold grows on food and other organic matter, and thus, breaks it down into slime by which it extracts nutrient for its growth. This is many times studied in school with a simple experiment.

Bread Mold Project

To study the growth of mold on bread samples every alternate day, for a course of 2 weeks.

If you are allergic to mold, then avoid performing this experiment or use mask and gloves for safety. Seek permission from your parents and teacher before you start with the experiment. Also, after you are done noting down the results of the experiment, dispose off the bags containing moldy bread safely, without opening them.

Here is a list of materials you will need to perform the experiment.

• 5 slices of bread
• 5 transparent sealable bags
• Sticky labels
• Magnifying glass
• 5 – 7 cotton swabs
• A tablespoon
• Lemon juice/water/apple juice/salt/sugar (at least two of these items are required)

Growing mold can be a simple experiment, and performed on a slice of bread. However, to make it interesting and more detailed you can work on 5 samples of breads rather than just one. So, gather the above equipment and follow the below steps.

• Take the cotton swabs and run them over areas which have dust, like under a table, bed, or basement.
• Then rub the dust from cotton swab over the first bread slice.
• Repeat steps 2 for the other four bread slices.
• Seal three bread slices inside three transparent sealable bags.
• Put sticker on the three bags, and write down using a marker on them.
• On the first sticker write “Sample #1 – Dark Closet”; on second write “Sample #2 – Refrigerator”, and on the third write “Sample #3 – Under Light”.
• So, keep the first sample in a dark closet, second in a corner of the refrigerator where it doesn’t gets disturbed, and the third one in an area of the house which is most of the time brightly lit.
• Now, take the remaining two samples. Before you seal them in the bags and mark them with sticker add one of the above mentioned five items to them. For example, on the fourth bread sample you can add some salt, while on the fifth you can add 2 tablespoons of water. Keep these two sample in a place where they don’t get disturbed.

Observations

Wear mask and gloves whenever observing the bread mold samples. Make sure you observe the five bread samples every alternate day at a fixed time of the day, say 2 pm. It is important that you observe them every alternate day without fail, and note down your observations in a table. You can note down their physical appearance like color, shape, amount of growth per day, texture, etc. Another column of your table can be observations of the mold under the magnifying glass. If you want, you can take videos or pictures of the mold every alternate day. This will help in concluding your experiment.

If you are performing this experiment at home, then you might not have access to a microscope. However, when this experiment is performed in school many times the students are asked to observe the mold under a microscope. Note down, the appearance of the mold under the microscope, this can form a part of the observation. Usually, one sees thread like structures on top of which there is a circular shape. Here is a diagram of bread mold in detail.

You will observe different conclusions for different samples. The mold which was kept in a warm, dark, and moist condition will grow the best. However, the sample that was in the refrigerator will have a slower growth. Also, substances like salt tend to slow down the growth of bread mold. Conclusion is an important part of the experiment, so make sure you read your observations carefully before you put down the appropriate conclusion of the project. Here are pictures of mold growth on different types of breads.

Further Experimentation

Once you have tried out this experiment, you can try out further experiments using different materials. You can try growing mold on different types of breads, while maintaining the same temperature. You could also try adding more moisture to the slices of the bread, or use different amounts of lemon juice and sugar on the slices. This way you can vary one element, and note down various observations of the mold growth. So, select a hypothesis and using the appropriate materials perform the experiment again. You can also consider growing mold on soft fruits. Here are pictures of mold growing on a lemon, few strawberries, and a tangerine.

Interesting Mold Facts

The above experiment will help to study bread mold in detail. Here are some fun facts about mold that will add to your knowledge.

Mold is used by various companies to make food and medicine.

Did you know that mold is added to flavor certain cheeses? You can observe blue-gray veins on a piece of blue cheese, which appear due to the mold added to it.

Lichens are formed due to an awesome partnership between fungi and algae.

There are over 10,000 species of mold!

Did you know that outdoors, mold is almost everywhere?

To prevent mold from growing on foodstuffs, the food industry spends a lot of money on refrigeration.

I hop you enjoyed reading the above facts on mold. So, gather the equipment necessary for the experiment, perform the experiment, note down the observations every alternate day, and draw the appropriate conclusion. Good luck!

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Bread Mold Experiment

Categories STEM Activities

We love classic science fair projects, which is why we have always wanted to try the classic bread mold experiment.

Although not as flashy as some of our other classic science fair projects, it was probably more educational than some others.

The students enjoyed seeing how long it took for mold to grow on various forms of bread. There is something really magical about those classic science experiments that have been done for generations! It’s fun to see each new generation learn something new each time they do the experiment.

Classic Bread Mold Experiment for Kids!

Follow along with these instructions to make your own version of the bread mould experiment!

Bread Mold Experiment Hypothesis Ideas

Kids should come up with their own hypothesis for the mold experiment. Have the children create a hypothesis something like this:

• Bread with preservatives will take longer to mold
• Bread in a sunny location will take longer to mold
• Warm bread will mold faster
• Wet bread will mold faster
• Bread will mold faster in the open air than in a plastic bag

Our experiment was simple. We placed bread in various conditions (we had dry dark, dry light, wet, open, and in a closed bag) and Monkey came up with a hypothesis for which piece of bread would mold first.

She predicted it would be the bread we placed in the paper bag in the pantry.

Mold Facts for Science Projects

When doing your bread mold science fair project, here are some fun mold facts for kids to include:

• Mold is a type of fungus.
• Mold grows in the shape or multicellular filaments called hyphae.
• Mold grows from spores that float in the air.
• There are thousands of types of mold, some good and some bad.
• A lot of cheese and antibiotics are created with a mold as a base.
• Mold is usually fuzzy.
• Mold is considered a single organism.

Bread Mold Experiment Materials

• Bread (fresh bread from a bakery will produce much faster results than bread with preservatives)
• Various bags
• A permanent marker to label each piece of bread

What You Need for a Science Fair

You’ll want to have these supplies on hand before doing your science fair project. Shop the included Amazon storefronts to make things easier and don’t forget to download the free science fair planning checklist before getting started!

Science Fair Project Planning

When you’re planning your project, you want to keep everything organized. Click the image below to get my free science fair project checklist so you can start organizing your project from the start.

You may also want to check out this list of science fair project research supplies.

Supplies for a Science Fair Project

There are so many supplies for science fair projects that are individual to each project, but if you want a general list of possible supplies and inspiration for your project, check out my selection of science fair experiment supplies on Amazon.

Supplies for a Science Fair Presentation

Your science fair presentation is important! It should look presentable and eye-catching. Check out this list of my favorite science fair presentation supplies.

Bread Mold Science Fair Project Directions

Divide your bread into as many pieces as you want to test. We used around five pieces.

We only put water on one of our bread pieces, but for the best “scientific” results, you should put water on one piece in a dark place and one in a light place.

In all, we had:

• Bread in a plastic bag in the light
• Bread in a plastic bag in the dark
• Bread in a paper bag in the dark
• Bread on a paper plate with no bag
• Wet bread in a plastic bag

My kids thought the dry bread in the paper bag would mold first.

You can take this project further by measuring how much mold is on each piece of bread after a certain number of days.

We just wanted to see which bread piece would mold first, so we did not do any mold measuring.

Bread Mould Experiment Results

It took about two days for the first mold to show up- which was on the wet piece.

We waited weeks for any mold to show up on any of the other pieces, but it didn’t. This is why we recommend using fresh bread without preservatives.

We finally gave up on waiting for any more mold to grow and threw it out.

The kids were surprised that the wet bread grew mold first, but she thought it was interesting that mold grows faster in damp, warm conditions.

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Bread Mold Experiment

Ever ended up with a loaf of moldy bread at home? It’s not something you want to eat! Instead, grow mold on bread for science, and investigate how moisture, temperature, and air affect mold growth. A fun and easy way to observe the mold life cycle for a hands-on biology experiment for kids .

Bread Mold Experiment Variations

Extend the learning by varying your experiment:

Remember only to change one variable for each experiment!

• Add the same amount of water to different types of bread.
• Place the same type of bread in light or dark conditions.
• Use the same type of bread and vary the amount of water on each.
• Place the same type of bread in a warm area and one in a cold area. Use a thermometer to work out the temperature.
• Place the same type of bread in a bag and one directly exposed to air.

Why not use extra slices of bread and set up this germ science experiment !

• 2 slices of bread

Instructions:

STEP 1: Label the plastic bags to identify each slice.

TIP: Don’t forget to make one or two predictions before you start. What do you think will happen to each slice?

STEP 2: Add 10 drops of water to one slice and seal.

STEP 3: Now add a dry piece of bread to the second bag.

STEP 4: Place the slices in a warm, dark place if possible. Observe and record.

Tip: Make observations every 2nd day over the course of 2 weeks depending on how fast the mold is growing.

Which piece of bread had the most mold on it? Make sure to read the science of mold to find out why.

The Science of Mold

Explores the fascinating world of fungi, like Rhizopus stolonifer, that often grow on bread with simple bread mold experiments. These tiny organisms love damp places so bread, with its moisture, is like a paradise.

Mold spores, everywhere in the air, land on the bread. When it’s warm, and there’s enough air and moisture, these spores grow into visible mold.

They grow quickly using special substances that break down the bread’s sugars. The fuzzy stuff you see on moldy bread is made of tiny threads called hyphae, which join together to form a network called mycelium. This helps the mold take in food from the bread.

Understanding bread mold helps us to see how fungi grows and shows how important conditions like warmth, air, and moisture are for these microorganisms to spread.

Turn It Into A Bread Mold Science Fair Project

Science projects are an excellent tool for older kiddos to show what they know about science! Plus, they can be used in all sorts of environments including classrooms, homeschool, and groups.

Kids can take everything they have learned about using the scientific method , stating a hypothesis, choosing variables , making observations and analyzing and presenting data.

Want to turn this experiment into an awesome science fair project? Check out these helpful resources.

• Science Project Tips From A Teacher
• Science Fair Board Ideas
• Easy Science Fair Projects

Free Printable Science Journal Worksheets

Create a science notebook with these easy-to-use science worksheets to accompany any experiment. Grab your free science process journal pack !

More Fun Biology Science Experiments To Try

• Investigate seed germination with a seed jar .
• Set up a mini-greenhouse .
• Make a model of your heart or of your lungs .
• Learn with animal cell and plant cell coloring sheets .
• Try this easy strawberry DNA lab.
• Set up a germ experiment.
• Explore the life cycles of various animals and plants .
• Candy DNA and coloring sheet.

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Growing Mold Science Experiment for Kids

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Have you ever wondered how dirty your house really is? I decided to try a little mold science experiment with my kids and see what things we need to do better at cleaning. But also, it was cool just to see how and where mold grows.

I was quite surprised by the results of our experiment. The kids and I had fun with this one, but is honestly gross to think about the amount of germs on the things we touch all of the time. Wash your hands!

How to Do the Mold Science Experiment

To do this gross science experiment you need unflavored gelatin , q-tips, and some sanitized containers (jars, plastic cups, petri dishes …).

Make the gelatin first. Boil 2 cups of water and prepare the gelatin according to the package directions. Stir the gelatin until it dissolves. Then pour it into your containers.

Make sure these containers are clean and not contaminated already. You don’t need much in each container. We used six different ones and just divided it evenly. We only had a couple of petri dishes, so we used a combo of the dishes and plastic cups.

Be sure your containers are sealed so no dust, debris or other organic material can get in ahead of the experiment.

Now you need to let the gelatin set, cooled and solidify. You will notice condensation and moisture as it cools. I waited a day before getting back to it, but it can be ready to use in just a few hours.

The next day, after the gelatin was set, we got a few q-tips wet and rubbed them on different surfaces throughout the house. We swabbed the trash can lid, the stove burner, the bathroom cabinet handle, one of my kid’s hands, the kitchen counter. Try your cell phones, door handles, TV remotes, etc. Anywhere will work, just try a variety of places to see different results.

After swabbing these different areas, label each cup and gently rub the q-tip all over the gelatin in the cup. You don’t want to break the surface of the gelatin, so do this carefully.

Cover them securely and set in a dark place for a time to allow the mold spores to grow. After a few days (even after just one day) mold will start to grow on the surfaces. We kept them growing for about a week to really see a large amount of mold growth.

We guessed ahead of time which areas we thought would be the dirtiest and grow the most mold. This is a great time to teach about a hypothesis. Try out our Scientific Method printable set for this!

I was dead wrong on our guess. I thought for sure that the trash can lid would be the worst, but from the results it seems my stove needs a good scrubbing!! Maybe there were food remnants on my stove that made it grow more? I’m not sure, but I gave it a good cleaning after finishing this experiment.

Have you ever tried the mold science experiment with your kids or students before? Try it out in your house or school and see what results you get. You may be unpleasantly surprised.

If you want an awesome book to pair with this activity, check out the book Fungus Is Among Us! by Joy Keller and Illustrated by Erica Salcedo. This book, published by Innovation Press (they make some of our favorite books!) is so much fun! It teaches kids about different types of Fungus growing and where you can find them.. You also can learn about a Mycologist (a scientist who studies fungi) in the back of the book.

More about mold science just for extra knowledge in your teaching:

Many wonder if mold is a bacteria or a fungus. Mold is part of the fungi kingdom.  It can grow on any organic materials. Mold reproduces with tiny spores that cannot be seen. They float through the air and land on wet surfaces. Mold can grow in places that have water damage or flooding, on foods, in an air conditioner, in wet carpeting, etc.

Frequent exposure to mold can cause a lot of harm to people, so it is important when doing a mold experiment that you do not inhale the mold spores. It can cause severe allergic reactions. Keep your face covered, or the mold covered at all times for safety.

See also the Rot Museum experiment!

Former school teacher turned homeschool mom of 4 kids. Loves creating awesome hands-on creative learning ideas to make learning engaging and memorable for all kids!

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14 comments.

I loooooove this! I am totally going to this. It’s so gross and awesome! What a great idea. Thanks you sharing!

I don’t even want to think about all of the germs on our counters.

This is as cool as it is gross! What a great way to keep kids interested while learning.

Thank you for stopping by the Thoughtful Spot Weekly Blog Hop this week. We hope to see you drop by our neck of the woods next week!

Bleh! I bet my kids would love that. 🙂

Good luck with your birth!!!

Okay, I wouldn’t be able to do this experiment. I am totally 100% freaked out by mold. I get rid of food that I suspect has been in the fridge more than 5 days and I try not to look at it. It gives me the Heebie Jeebies.

Just looking at the pictures makes me shreek.

Thanks for linking up this nasty post to the #homeschoollinkup! It’s a totally fun experiment – but gross to look at mold.

Ha ha, Lisa! You are so funny. It is pretty gross, but at least it was contained 😉

That is both gross and cool at the same time. Funny how the places we think of as dirty were the cleanest. Probably because we tend to clean them more often. Thanks for sharing via Family Fun Friday.

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My 10 yr old daughter did this experiment for her science project. It was amazing. I had bought a kit that did the samething and it did not work as well and was so much more expensive. She got an A+ for this. Thank you so much for the directions and and all the information.

Hello! I was wondering if you had any photos of her results? I’m a 1st grade teacher and am thinking about doing this in my classroom! [email protected]

I am trying this experiment this week and nothing is growing. What could I have done wrong ????

Maybe you are a better cleaner than me! 😉 it actually took a while & it worked best in a dark location.

We did this with our Creative Tots Mason Preschoolers and they absolutely loved it! Thank you for sharing this with us!

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Temperature versus Relative Humidity: Which Is More Important for Indoor Mold Prevention?

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Temperature is known as one of the abiotic factors that can affect mold growth. Many mold growth prediction models consider temperature as one of the parameters that can significantly impact mold growth indoors, and hence temperature has been targeted by different indoor mold prevention strategies on different premises. For example, European guidelines for libraries suggest a temperature of 19 °C to preserve books. However, running low temperature air-conditioning (AC) costs substantially more energy, and thus a higher temperature (e.g., 25.5 °C) has been regularly proposed as the recommended indoor temperature for general indoor environments in Hong Kong. It is, therefore, needed to understand whether or not the reduction of indoor temperature would lead to better effectiveness of mold prevention. Using Cladosporium cladosporioides ( C. cladosporioides ) as the model, its germinating spores were challenged in C. cladosporioides to wet-dry cycles with different combinations of relative humidity (RH, 40%, 60% and 80%) and temperature (19 °C and 28 °C) levels. The survival, lipid peroxidation and catalase (CAT) activity of the treated spores were monitored and compared. C. cladosporioides spores showed similar levels of viability, lipid peroxidation and CAT activity when they were exposed to 19 °C and 28 °C at the same RH, but substantially lower survival and higher oxidative stress were observed under the wet-dry cycles with 40% RH dry periods compared with 60% and 80% RH at both temperatures, suggesting that indoor temperature does not tend to affect the resistance of C. cladosporioides to wet-dry cycles as significantly as the RH level of the dry period. Collectively, this study suggests a more important role for moisture over temperature in indoor mold prevention. The outcome of this study may facilitate the sustainable management of indoor mold problems in buildings.

1. Introduction

Due to the adverse health effects brought by molds, building scientists have developed mold growth models to predict mold development under different environmental conditions. As indicated by the growth models, temperature is one of the abiotic factors proven to significantly affect mold growth [ 1 ]. Therefore, temperature has been one of the targets for mold control in indoor environments [ 2 ].

As one of the important factors affecting mold growth, the temperature effect has been widely investigated by researchers. The investigations of the temperature effect were initiated under a constant state, which focused on the impacts on indoor mold growth brought by different temperature levels [ 1 , 3 , 4 ]. Moreover, the production of mycotoxins was also found to be significantly affected by temperature [ 5 ], highlighting the need for considering temperature as one of the factors that would not only affect mold growth but also potentially compromise human health if it is not properly maintained. Later, upon realizing that constant states of temperature are artificial environments in laboratories rather than real-world situations, researchers began to place more focus on the effects of cyclic temperature levels on the growth of indoor molds. Johannson et al. (2013) exposed mold spores to transient temperature conditions and drew the conclusion that dynamic temperature appeared to slow down mold growth compared with steady-state temperature levels [ 6 ]. These previous studies tend to support the important role of temperature in influencing the responses of molds.

European guidelines suggest a temperature range of 19–24 °C for preserving paper products. In particular, for premises where important materials are stored; e.g., libraries, the temperature is usually maintained at relatively low levels (e.g., at around 19 °C) to slow down mold activities, in order to protect paper materials from fungal deterioration [ 7 ]. As per the updated VTT model developed by Ojanen et al. (2010), molds take significantly longer to germinate at 19 °C compared with 25.5 °C on building materials that are sensitive to mold growth [ 1 ]. Therefore, maintaining a low temperature has been widely believed to be effective at preventing indoor mold contamination. However, the facility management team for university campuses on occasion receives complaints from students regarding the low temperature in the library. It is reported that a drop of 1 °C in the room temperature consumes 3% more energy [ 8 ], and simultaneously, the operation of ACs emits carbon dioxide (CO 2 ) which would accelerate global warming. Therefore, in order to balance indoor mold hygiene and environmental sustainability, it is necessary to investigate if such a low temperature is needed to be maintained in particular venues.

The aim of this study is to investigate the effect of temperature on the resistance of indoor molds to wet-dry cycles, so as to understand the necessity of maintaining a costly low temperature indoor environment. In this study, using Cladosporium cladosporioides ( C. cladosporioides ) as the model, its germinating spores were exposed to wet-dry cycles with the combination of two temperatures (19 °C and 28 °C) and three relative humidity (RH) levels (40%, 60% and 80%). The two tested temperature levels, 19 °C and 28 °C represent the low temperature in libraries and unconditioned atmospheric temperature, respectively; meanwhile, 40% and 60% RH mimic the lowest and normal indoor humidity that air-conditioning units or dehumidifiers can maintain, and 80% is a common unconditioned atmospheric RH level. Afterward, the germination percentage, lipid peroxidation level and CAT activity of the treated molds were measured and compared. The results of this study help to facilitate the sustainable management of mold hygiene problems in buildings.

2. Materials and Methods

2.1. tested organisms and growth conditions.

C. cladosporioides stain ATCC ® 16022™ was ordered from the American Type Culture Collection (ATCC; Manassas, Va, USA) and used in our experiments due to its common isolation from indoor environments and role as a model mold species for standard tests [ 9 ]. Mold cultures were routinely grown on malt extract agar (MEA; HKM, Guangzhou, China) plates at 28 °C for a week prior to the experiments.

2.2. Mold Survival under Moisture Dynamics

The experimental setup used in this study is similar to the one detailed previously [ 10 , 11 ]. Briefly, spores of C. cladosporioides were harvested, washed and enumerated according to the standardized method [ 12 ]. Afterward, 100 μL of spore suspension with a density of 1 × 10 6 spores/mL was inoculated onto a cellulose membrane (47 mm diameter, 0.2 μm pore size) overlying a 0.99 water activity (a w , equivalent to 99% RH) MEA plate. Inoculated spores were spread out homogeneously using a disposable plastic spreader, then cultured in the isotropic swollen stage (confirmed by a light-microscope). Afterward, membranes with swollen spores were transferred to low a w MEA plates (0.4 a w , 0.6 a w or 0.8 a w ) and incubated under 40%, 60%, or 80% RH for up to 15 days at either temperature (19 °C or 28 °C) in a digital hygrothermal incubator (Bluepard, Shanghai, China). The adjustment of the a w levels of agar plates was achieved by supplementing glycerol [ 10 ]. Next, membranes with spores were re-exposed to wet conditions (0.99 a w , 28 °C) for up to one month to assess their viability. These wet-dry cycles are termed as moisture dynamics. Spores able to form a germ tube longer than or equal to their longest dimension after exposure to moisture dynamics were defined as viable. Germination percentage was used to present the viability of spores exposed to moisture dynamics, which was assessed by cutting 1 cm 2 of the membrane and counting the percentage of germinated spores under a light-microscope during re-exposure to the wet condition.

2.3. Quantification of Oxidative Stress

Elevated oxidative stress leads to the generation of reactive oxygen species (ROS), and thus damages cell lipids. As a consequence of oxidative damage, the lipid peroxidation level of dried molds was measured with a Lipid Peroxidation (MDA) Assay Kit (Abcam) following the protocol provided by the manufacturer, which assesses the formation of malondialdehyde (MDA) in mold samples. Immediately upon the completion of wet-dry cycles, treated mold spores were moved into sterile ultrapure water immediately and subjected to homogenization. The determined MDA concentration in mold samples was then normalized with the protein concentration present in the samples, which was quantified using a Pierce TM BCA Protein Assay Kit (Thermo Fisher Scientific, Waltham, MA, USA).

2.4. Characterisation of Antioxidant Responses

CAT is the key antioxidant enzyme produced to decompose H 2 O 2 oxidative stress. As confirmed in our previous study, catalase (CAT) is the most significantly changed antioxidant enzyme in response to moisture dynamics [ 11 ]. Therefore, CAT activity was used to represent antioxidant responses in this study. The CAT activity of treated molds was quantified using a Catalase Assay Kit purchased from Cayman Chemical (Ann Arbor, MI, USA) following the protocol suggested by the manufacturer. Catalase activities of all samples were minimized with the protein concentration.

2.5. Statistical Analyses

The differences in the levels of lipid peroxidation and CAT activity in C. cladosporioides under different temperature and RH levels were compared using repeated measures of one-way analysis of variance (ANOVA) with Duncan’s post hoc test in SPSS v.24, in order to determine whether significant differences in oxidative stress and antioxidant response were found between the tested mold species. Differences between means with a p -value lower than 0.05 ( p < 0.05) were regarded as statistically significant.

3.1. Viability of C. cladosporioides under Moisture Dynamics

C. cladosporioides spores were cultured to the isotropic swollen stage prior to the exposure to different water conditions. The mean length of swollen spores measured in this study is 7.64 μm (± 0.18 μm SD), which is comparable to 7.51 ± 0.96 μm in Quintana-Obregón et al.’s (2011) study [ 13 ]. Over 80% of spores were at a synchronized developmental stage.

The germination percentage of the dehydrated mold spores was used as an indicator to assess mold viability. The viability of C. cladosporioides spores under moisture dynamics with different combinations of temperature and RH levels is presented in Figure 1 .

The germination percentage of C. cladosporioides spores exposed to moisture dynamics with different combinations of RH and temperature levels. The changes in germination percentage under moisture dynamics were analyzed by repeated measures one-way ANOVA. Grouping was performed by Duncan’s post-hoc test. Letters in parentheses indicate different groupings.

The viability of C. cladosporioides decreased as the drying time extended at both 19 °C and 28 °C when they were exposed to wet-dry cycles with dry periods at 40% and 60% RH; meanwhile, there was not a significant decrease in viability when molds were incubated under 80% RH. Similarly, there was no significant difference found in the survival of C. cladosporioides between 19 °C and 28 °C when the RH was fixed, but 40% RH led to significantly lower viability in C. cladosporioides than 60% and 80% RH at both temperature levels.

The lowest survival was determined when C. cladosporioides was incubated under 40% RH dry periods. The viability of molds dropped sharply to 47% at 19 °C and 55% at 28 °C after 1 day, then to 15% at 19 °C and 22% at 28 °C upon 3-day-drying. After 5 days, all the spores dehydrated under 40% RH at 19 °C and 28 °C were inactivated and no resumption of growth could be observed followed by subsequent rewetting. When dry periods of 60% RH were adopted, for both temperature levels, the viability of C. cladosporioides declined to approximately 80% after the first 3 days. Then, the most dramatic reduction in the viability of C. cladosporioides was observed between the and fifth day, where the survival of mold spores dropped to 20%. All spores were inactivated when the dry periods were further extended to 7 days for 19 °C and 28 °C.

In contrast, dry periods of 80% RH at neither 19 °C nor 28 °C appeared to inactivate C. cladosporioides spores within 15 days. Similar survival was observed throughout the 15-day dry periods and almost all treated spores at 19 °C and 28 °C restored growth after a 15-day 80% RH period. Overall, C. cladosporioides spores subjected to wet-dry cycles showed similar levels of survival between 19 °C and 28 °C when the same RH level was maintained while significantly lower viability was observed when the RH was reduced to 40% compared with 60% and 80% at both temperatures.

3.2. Oxidative Stress Encountered in C. cladosporioides under Moisture Dynamics

Lipid peroxidation has been demonstrated to give a clear indication of the oxidative damage encountered by molds; thus, the formation of MDA, which is used to reflect lipid peroxidation level, was monitored in C. cladosporioides spores in the present study. Results are shown in Figure 2 .

Lipid peroxidation level of C. cladosporioides spores exposed to moisture dynamics with different combinations of RH and temperature levels. The changes in MDA concentration under moisture dynamics were analyzed by repeated measures one-way-ANOVA. Grouping was performed by Duncan’s post-hoc test. Letters in parentheses indicate different groupings.

Under wet conditions (99% RH, 0 days), C. cladosporioides formed a low background level of MDA concentration, which was approximately 30 nmol/min/mg protein. A substantial increase in MDA concentration was measured when 40% or 60% dry periods were introduced at 19 °C and 28 °C. General climbing trends in MDA concentration were observed for dry periods of 40% and 60% RH at both tested temperatures.

The highest MDA formation was detected in C. cladosporioides incubated under 40% RH dry periods. In a one-day 40% RH period, MDA concentration increased to 411 nmol/min/mg protein at 19 °C and 553 nmol/min/mg protein at 28 °C. MDA concentration reached 1100 nmol/min/mg protein at 19 °C and almost 1168 nmol/min/mg protein at 28 °C after the fifth day. For both temperatures at the 60% RH, the concentration of MDA in C. cladosporioides was approximately 130 nmol/min/mg protein upon the first day of drying and gradually ascended to over 300 nmol/min/mg protein after 7 days.

With respect to C. cladosporioides spores incubated at 80% RH, the lipid peroxidation level at both tested temperatures tended to be much lower than at 40% and 60% RH. A flattening change in MDA concentration (around 40 nmol/min/mg protein) was measured for both 19 °C and 28 °C, which was similar to the control wet condition (99% RH). Generally, the formation of MDA in C. cladosporioides spores was similar between 19 °C and 28 °C, when the RH was fixed, but a markedly higher MDA concentration was determined in C. cladosporioides spores exposed to lower RH levels.

3.3. CAT Activity of C. cladosporioides under Moisture Dynamics

As an important antioxidant enzyme produced to detoxify oxidative stress, CAT activity was monitored in C. cladosporioides under wet-dry cycles and is shown in Figure 3 .

CAT activity of C. cladosporioides spores under wet-dry cycles with different combinations of RH and temperature. The changes in CAT concentration under moisture dynamics were analyzed by repeated measures one-way ANOVA. Grouping was performed by Duncan’s post-hoc test. Letters in parentheses indicate different groupings.

Under control conditions (0 day), very low (2 U/ mg protein) CAT activity was found in C. cladosporioides , and all tested combinations of wet-dry cycles considerably induced CAT activity in C. cladosporioides .

When dry periods of 40% and 60% RH at 19 °C and 28 °C were introduced, the CAT activity of C. cladosporioides increased to around 260 U/mg for all of the four tested combinations and remained insignificantly different during the incubation under dry periods. At an RH of 80%, there were significant increases in CAT activities when compared with the background level, but the level of CAT activities detected in C. cladosporioides was approximately 95 U/mg protein for both temperatures, which was markedly lower than that measured under 40% and 60% RH. Generally, the CAT activities achieved by C. cladosporioides under 40% and 60% RH at 19 °C and 28 °C were similar and found to be higher than the CAT activities detected under the wet-dry cycles with a RH of 80% RH (19 °C, 80% RH and 28 °C, 80% RH).

4. Discussion

Extensive studies have demonstrated that molds accelerate their growth rate when the temperature approaches the optimum level [ 4 , 14 ], and thus, all mold growth prediction models take temperature into account when the growth of molds needs to be predicted [ 1 , 4 ]. However, temperature is also an important factor influencing occupants’ comfort, and therefore, should be kept within a certain range; an “Excellent” level of indoor air quality (IAQ) requires an indoor temperature between 20 °C and 25.5 °C. In Hong Kong, in light of sustainability, 25.5 °C has been regularly proposed to be a recommended temperature for air-conditioning (AC) systems. As one of the special cases, low temperature is usually maintained in libraries for the sake of book preservation. The low temperature of 19 °C is suggested by European guidelines to preserve books, which could cost nearly 20% more energy compared with 25.5 °C. Determining whether or not it is necessary to run such an energy-consuming mold prevention strategy is useful. The findings of this study may help in developing a more sustainable and reasonable AC management regime for mold prevention in indoor environments, especially libraries.

4.1. Insignificantly Different Resistance to Wet-Dry Cycles between 19 °C and 28 °C

As shown in Figure 1 and Figure 2 , C. cladosporioides spores did not show significantly different tolerance toward wet-dry cycles between 19 °C and 28 °C, as reflected in the similar viability and lipid peroxidation levels. The temperatures of 19 °C and 28 °C represent typical low and unconditioned indoor levels, respectively. The insignificantly different tolerance towards wet-dry cycles revealed in this study implies that indoor temperature does not tend to significantly affect the effectiveness of mold prevention, suggesting that temperature control is not an effective approach and it may not be necessary to maintain a low temperature in indoor environments.

Although this is the first study to investigate the effects of temperature on the resistance of indoor molds to wet-dry cycles, making the results not directly comparable to other work, the insignificant role of indoor temperature revealed in this study meets the expectations of Aihara et al. (2002) and other mold growth models [ 4 , 14 ]. It is reported that C. cladosporioides showed similar resistance to suboptimal moisture conditions within the range of 19 °C to 28 °C. Moreover, the isopleth model also supports the finding that mold growth rate is similar at 19 °C and 28 °C for all tested RH levels.

Notably, the above-referenced studies that examined temperature effects were conducted under constant moisture conditions, and the influence of indoor temperature on the tolerance of indoor molds towards wet-dry cycles has not been explored. Some mold growth models (e.g., the VTT model) indicate a significantly slower growth at 19 °C compared with 28 °C, which may over-emphasize the necessity for maintaining a low indoor temperature [ 1 ]. In reality, the water supply for molds in indoor environments can fluctuate substantially because of occupants’ activities, such as cooking and showering, and therefore, the temperature effect revealed under constant water conditions is not sufficient for understanding its role in real-world building contexts. The findings of our current study hint that the significance of the temperature effect tends to be less than expected and it is more important to run a wet-dry cycle regime with low RH periods for the purpose of indoor mold prevention.

4.2. Relative Humidity of Dry Periods Is More Critical Than Temperature for Mold Prevention in Indoor Environments

According to Figure 1 and Figure 2 , when the relative humidity was fixed at 60% RH, C. cladosporioides spores did not exhibit markedly different viability and lipid peroxidation levels between 19 °C and 28 °C, suggesting that C. cladosporioides encountered similar oxidative stress at these temperature levels under wet-dry cycles. However, when the temperature was maintained at either 19 °C or 28 °C, C. cladosporioides displayed substantially lower survival and higher lipid peroxidation levels at 40% RH compared with 60% and 80% RH. These results suggest that within the indoor context, the importance of the RH in dry periods tends to be higher than the temperature, strengthening the observation that RH is a more important factor in determining mold survival when compared to temperature in the indoor environment.

Although no researcher has compared the impacts brought by temperature to RH on the tolerance of indoor molds to wet-dry cycles, the expectation that the degree of water stress (i.e., RH) is more significant than the temperature suggested by this study is consistent with others’ work. It was reported by Aihara et al. (2002) that a reduction of 0.01 a w (i.e., 1% RH) appeared to significantly delay the growth of C. cladosporioides and C. sphaerospermum , whereas a decrease of 6 °C was required to acquire the same growth delay. Briceño and Latorre (2008) also observed a higher growth rate at 0.98 a w than 0.96 a w (equivalent to the difference of 2% RH) in C. cladosporioides and Cladosporium herbarum [ 15 ]. In addition, Krus et al. (2007) showed that only when the temperature was 10 °C apart from the optimum level, a significant difference could be observed, while a 5% lower RH was able to yield an observable slower growth rate [ 16 ]. The results of these studies help support the insignificant differences in survival observed in the current work.

It is worth mentioning that although 40% RH was demonstrated to cause lower viability and severe oxidative stress in C. cladosporioides , this knowledge does not necessarily bind a lower RH to a more detrimental consequence or higher stress level. Wyatt et al. (2015) observed a better survival of two fungi, Talaromyces macrosporus and Neosartorya fischeri , under stringently dried conditions (0% RH) compared with air dried at 40–60% RH [ 17 ]. Segers et al. (2016) believed that this was because of the low mobility of molecules at 0% RH, which suppressed the detrimental chemical reactions [ 12 ]. Therefore, some extreme conditions may to some extent act as a protective effect against ambient stresses, and thus, it is not a definite rule that lower a w or RH will contribute to a more stressful environment.

4.3. Similar CAT Activity Determined at 19 and 28 °C May Explain the Insignificant Effect of Temperature under Moisture Dynamics

Temperature is known to impact the metabolic activity of microorganisms by affecting their enzyme activities. Enzymes peak their activities at optimum working temperature, and therefore, the suboptimal temperature would reduce the protective effect of enzymes when microbes encounter unfavorable environments. Tang et al. (2007) agreed that shifts in ambient temperature could reduce the survival of airborne bacteria because the changing temperature affects enzyme activities and consequently impacts the metabolic activity and viability of microbes [ 18 ].

Indoor molds typically peak their growth between 25 °C and 30 °C, which implies that the enzymes of the majority of indoor molds may exhibit an optimum working efficiency within this temperature range. As shown in Figure 2 , except for the case of 80% RH, CAT activities carried by C. cladosporioides under a RH of 40% or 60% RH as well as a temperature of 19 °C or 28 °C were similar. Although 40% RH caused much higher oxidative stress and lower survival, the CAT activities measured, resembled those under an RH of 60%, suggesting that dry periods of 60% RH have already induced the maximum capacity of the CAT enzyme, and hence even when a more stressful RH level (40% RH) was introduced, the defense (CAT activity) still remained similar. The unobservable difference in the CAT activity alongside the similar oxidative stress encountered determined in Figure 2 and Figure 3 may help explain the insignificant effect of temperature on the resistance of C. cladosporioides to wet-dry cycles—when the stress and defense level remain insignificantly different, the consequences (viability, representing resistance to wet-dry cycles) would also likely be similar. On the other hand, since 60% RH has already induced the maximum capacity of the CAT enzyme in C. Cladosporioides , when the RH was reduced to 40% and severer stress was imposed, lower viability was expected. Therefore, it also makes sense that 40% RH yielded lower viability in C. cladosporioides compared with 60% and 80% RH.

4.4. Implications of the Study

Libraries normally store numerous special collections, and hence the management team would choose to minimize the risk of fungal contamination. According to some mold growth models, e.g., the updated VTT model, a lower temperature can further slowdown mold activities, and consequently, a low temperature is usually maintained in libraries. From time to time, complaints regarding the low temperature in libraries have been experienced. Many management teams have published announcements and explanations on the low temperature maintained in libraries. As a large part of operation costs, the AC accounts for over 30% of building maintenance charges [ 8 ]. Furthermore, several libraries operate continuous AC to minimize the risk of mold outbreaks [ 7 ], which would lead to an even higher cost if the low temperature is also maintained.

However, the results of this study stress the necessity of running ACs in a constant low temperature mode as long as the humidity is properly maintained. Figure 1 and Figure 2 indicate insignificant differences in survival and oxidative stress encountered between 19 °C and 28 °C when C. cladosporioides spores were exposed to wet-dry cycles; while dry periods at a lower RH rendered markedly lower mold viability and higher encountered oxidative stress, which implies that the reduction of indoor humidity would probably contribute to a better mold prevention effectiveness than running ACs at cold temperature.

In addition, two commonly found indoor molds, C. cladosporioides and Cladosporium halotolerans , are known to be psychrotolerant [ 9 ]. They have been isolated from cold environments, such as fridges and arctic regions, respectively, which may be a sign that these mold species are able to maintain proper enzymatic activity even when the environment is unfavorably cold. The lowest acceptable temperature is ascertained to be 19 °C, and the insignificant effect imposed by 19 °C on mold survival under wet-dry cycles compared with 28 °C revealed in this study may be extrapolated to other common indoor molds, such as C. halotolerans , which further challenges the effectiveness of temperature control.

Given that indoor temperature does not tend to be as critical, it may be feasible to use dehumidifiers instead of ACs to achieve moisture control in order to save energy. The use of dehumidifiers to replace ACs is not limited to libraries and could also be applied to other indoor environments, such as offices and residential areas. In a typical 20 m 2 office, a 280 Watts-hour dehumidifier only accounts for 34% of the costs caused by AC operation (using 1.5-ton AC as an example). Hence, the facility management team may consider operating ACs at a higher temperature (e.g., 25 °C during office hours for occupants and temperature levels that do not require cooling after office hours) or using dehumidifiers instead to balance sustainability and mold hygiene.

5. Conclusions

In this study, C. cladosporioides spores were challenged in wet-dry cycles with different combinations of RH (40%, 60% and 80%) and temperature levels (19 °C and 28 °C). We present insignificant differences in the viability, lipid peroxidation levels and CAT activity of C. cladosporioides between the two tested temperature levels under wet-dry cycles. When the temperature was fixed at either 19 °C or 28 °C, markedly higher oxidative stress and lower viability in C. cladosporioides spores were found at 40% RH compared with 60% and 80% RH. The results stress the necessity of maintaining a low temperature in indoor environments, such as libraries and imply that moisture control tends to be more crucial than maintaining a cold environment for the sake of indoor mold prevention.

Funding Statement

This research received no external funding.

Author Contributions

Conceptualization, H.W. and J.W.C.W.; methodology, H.W.; formal analysis, H.W.; investigation, H.W.; resources, J.W.C.W.; writing—original draft preparation, H.W.; writing—review and editing, H.W. and J.W.C.W.; supervision, J.W.C.W. All authors have read and agreed to the published version of the manuscript.

Data Availability Statement

Conflicts of interest.

The authors declare no conflict of interest.

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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• Published: 17 June 2021

Increased duration of pollen and mold exposure are linked to climate change

• Bibek Paudel 1 ,
• Theodore Chu 2 ,
• Meng Chen 1 ,
• Vanitha Sampath 1 ,
• Mary Prunicki 1   na1 &
• Kari C. Nadeau 1   na1  

Scientific Reports volume  11 , Article number:  12816 ( 2021 ) Cite this article

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• Climate change
• Environmental impact

Pollen and molds are environmental allergens that are affected by climate change. As pollen and molds exhibit geographical variations, we sought to understand the impact of climate change (temperature, carbon dioxide (CO 2 ), precipitation, smoke exposure) on common pollen and molds in the San Francisco Bay Area, one of the largest urban areas in the United States. When using time-series regression models between 2002 and 2019, the annual average number of weeks with pollen concentrations higher than zero increased over time. For tree pollens, the average increase in this duration was 0.47 weeks and 0.51 weeks for mold spores. Associations between mold, pollen and meteorological data (e.g., precipitation, temperature, atmospheric CO 2 , and area covered by wildfire smoke) were analyzed using the autoregressive integrated moving average model. We found that peak concentrations of weed and tree pollens were positively associated with temperature ( p  < 0.05 at lag 0–1, 0–4, and 0–12 weeks) and precipitation ( p  < 0.05 at lag 0–4, 0–12, and 0–24 weeks) changes, respectively. We did not find clear associations between pollen concentrations and CO 2 levels or wildfire smoke exposure. This study’s findings suggest that spore and pollen activities are related to changes in observed climate change variables.

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Introduction.

Climate change, brought about by increased human activity in the last few decades, has a number of effects on planetary and human health 1 . Increased human activity has led to increases in a number of greenhouse gases such as carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), and ozone (O 3 ). The global average atmospheric CO 2 in 2018 was 407.4 parts ppm, which are higher than at any point in at least the past 800,000 years 2 . Global average temperature increased by about 1.0 °C from 1901 to 2016 3 and continues to increase. The last 5 years, 2015–2019, have been the hottest years ever recorded. Climate change has led to increases in extreme weather events, such as increased flooding, wildfires, and thunderstorms 4 . The Centers for Disease Control and Prevention lists health effects of climate change including increased risk of atopic diseases such as allergic rhinitis and allergic asthma 5 . This trend is especially concerning due to the high prevalence of atopic disorders. Currently, approximately a quarter of individuals in developed countries 6 are affected by allergic disease and these numbers are expected to increase with climate change. Temperature, rainfall, and other variables of climate change have been shown to indirectly effect allergies and asthma by their effects on pollen and molds 7 , 8 . Pollen from trees, grasses, and weeds and spores from mold are sources of allergens. Changes in vegetation, increased pollen/mold spore concentrations, and prolonged pollen seasons are linked to climate change. Increases in pollen/mold spores from climate change lead to allergies and asthma; the effects of climate change on human health is well documented 9 , especially in case of allergies 10 . For example, the distribution of the common ragweed ( Ambrosia artemisiifolia L ) has been expanding from Central to Northern and Eastern Europe due to changes in climate (rising temperatures, favorable precipitation) and that increases in CO 2 has been increasing ragweed pollen production and allergies in these regions 11 . Following thunderstorms, a record-breaking number of visits to the emergency department for respiratory issues was observed in Australia in 2016 12 . During thunderstorms, whole pollen grains are swept into the clouds where they are broken up into smaller allergenic pollen fragments and eventually carried back to ground level 13 . These smaller size of pollen fragments permit their entry deep into the lungs. The mechanisms hypothesized for the fragmentation of pollen during thunderstorms include mechanical friction from wind gusts, electrical build up and discharge incurred during conditions of low relative humidity, and lightning strikes 14 . Air pollutants and CO 2 levels have also been shown to affect the prevalence of aeroallergens 15 .

Airborne pollen and mold contribute significantly to adverse health outcomes in allergy and asthma. Increased pollen counts in spring is associated with increases in over-the-counter allergy medication sales and increases in emergency visits due to asthma exacerbations 16 , 17 . Pollen and molds are key triggers for allergic rhinoconjunctivitis and asthma flares. Increases in molds, caused by heavier rainfall and higher temperatures, can cause respiratory and asthma-related conditions as well as allergic bronchopulmonary aspergillosis, allergic fungal rhinosinusitis, and hypersensitivity pneumonitis 18 . There is also growing evidence that changes in the climate may be contributing to the rising incidence of food allergy due to changes in distribution of sensitizing plants and possibly due to a direct alteration in the allergenicity of plants with rising CO 2 levels 19 . Since different patients are sensitive to different levels of atmospheric allergens, it is important to understand how the pollen and mold activities are changing over time. Patients who are sensitive to even small amounts of pollen and mold spores could benefit from the knowledge of their activities and outside peak allergy seasons, and how they vary with climate change.

As pollen and molds exhibit geographical variations, we sought to understand the effects of climate on common environmental pollens and mold spores in a specific region in the San Francisco Bay Area (Los Altos Hills, CA). In addition to measurements for maximum temperature, carbon dioxide level, and precipitation, we also compare the change in pollen or mold spore concentration with wildfire smoke exposure, as our area of study has been experiencing increasing exposure to wildfire smoke in recent years. An important gauge of the impact of climate change lies in phenology of pollen and mold exposure due to changes in pollen seasons and intensity of exposures 20 , 21 , 22 , 23 . We therefore evaluated a long-term dataset of outdoor pollen and mold observations over an 18-year period (2002–2019) using an in-depth analysis across the spectrum of aeroallergens (tree, grass and weed pollens and mold spores) contributing to allergic disease. The region is bounded by the Santa Cruz mountain range to the west and the San Francisco Bay to the east and has a Mediterranean climate. It is one of the most populated ecoregions in the United States and lies within the San Francisco-San Jose metropolitan area 24 . The average land change footprint of the area between 1973 and 2000 as determined by 11 land-cover classes (eg., mining, forest, agriculture, wetland) was estimated at 9.9% 24 . The vegetation is a mixture of grasslands, shrublands, and various forest types, the dominant among which is the evergreen forest 25 . In addition to the mixed evergreen forests, the coastal areas are covered by coastal scrub 26 . The region is undergoing changes in land cover due to rapid urbanization. A 19-year study (1984–2002) found that that the population increased by 30% and the urban area increased by 73%, leading to a 17% increase in impervious land cover and a 27% decrease in pervious surfaces 27 .

Annual and seasonal trend analysis

A summary of the terminologies to measures pollen and spore activity are presented in Table 1 and described in Methods .

For all three groups major allergens, selected species, and commonly observed species ( Methods ), we analyzed annual trends in pollen and mold concentrations, seasonality, and activity. All statistical analyses were performed in the Python programming environment (Python Software Foundation, http://www.python.org ) and p values < 0.05 were considered statistically significant.

Summary statistics for annual and seasonal characteristics of major allergens is presented in Table 2 . The week on which pollen concentrations peak for each type of allergen is given in the “Peak Week” column, which shows the distinct seasonal pattern of each type of major allergen. Tree pollens peak in Spring, Grass pollens peak in late Spring and early Summer, Weed pollens peak in Summer, and Mold concentrations peak in Fall. To quantify various annual trends for each observation, the annual average values for major allergens as well as the annual trends for the different climate variables were analyzed and plotted (Supplementary Figs. S1 and S2 ). Statistical significance was calculated by fitting linear trends using first-order linear regression. Supplementary Fig. S3 shows statistically significant increasing trends for T Max and CO 2, while there was no such trend for precipitation. In Supplementary Table S1 - S3 , we present the temporal trends for major allergens, selected species, and most commonly observed species. A decreasing trend for major allergens’ annual average concentrations (statistically significant for trees and grasses, coefficients of linear trend: − 3.16 and − 0.19 respectively) were observed (Supplementary Table S1 ). Although the annual average concentrations for all major allergens except weeds showed a decreasing trend, only tree and grass pollens were statistically significant with p value < 0.05. For details about individual tree, weed, grass, and mold species refer to Fig.  2 and Supplementary Tables S3 - S5 . We also analyzed changing season length for different pollen and mold spore types over the years. We found increases in the season length for tree pollens (0.38 weeks). Given the increasing season lengths for some pollen despite the decrease in average annual pollen counts, the number of active weeks was also investigated. The annual linear trends for these values are shown in the third column of Supplementary Table S1 - S3 . The number of active weeks significantly increased for tree pollens and molds. To examine whether pollen and mold seasons were starting sooner and extending further into the year, the weeks of the year when the pollen seasons and mold seasons start and end were calculated (seasons were calculated using an established procedure, Methods ); the coefficients of linear trends are shown in the fourth and fifth columns of Supplementary Tables S1 - S3 . For tree pollens, we observed a significant delay in the end of season (0.29 weeks).

Supplementary Tables S2 and S3 reveal interesting properties regarding annual concentrations, which are different from what was observed for major pollens and mold. For both mold and weed species, there were increases in annual average concentrations (although not statistically significant), while all tree species show a decreasing trend. The pollen season is getting longer and starting earlier for a majority of species, but the trends were not statistically significant. Similarly, the season is ending later for a majority of species, but the trend was not statistically significant. In Supplementary Table S3 , the most commonly observed species (all of which are molds) demonstrate increasing trends for the number of active weeks. The top-two most commonly observed species were active for an average of half a week more than prior years. In Figs.  1 and 2 , we visually show the change in seasonal characteristics and number of active weeks for major allergens, and commonly observed species. In Supplementary Fig. S1 , we visually show these results for those selected species whose season length we were able to calculate for at least 10 years during our study duration.

Coefficient estimates and 95% confidence intervals for change in season length, number of active weeks, start of season, and end of season for Major allergens.

Coefficient estimates and 95% confidence intervals for change in season length, number of active weeks, start of season, and end of season for the most commonly observed species. Italics: Trees , Normal: Molds, Bold: Weeds.

Association of pollen counts with climate variables

To study the association of pollen concentrations with patterns of climate variables, the well-established autoregressive method Auto Regressive Integrated Moving Average (ARIMA) was used. For details on ARIMA, please refer to the Methods section.

Associations of pollen and mold with three climate variables (maximum temperature, precipitation, carbon-dioxide, and smoke area) are shown in Table 3 . The columns in the table show the association of climate variables in different lags, e.g., T Max (0–24) shows the association of maximum temperature in prior six months on the pollen and mold concentrations. In other words, these values show how peak pollen and mold concentrations are related to the lagged values of different climate variables. Climate variables immediately before, as well as a year before could be strongly associated with pollen and mold concentrations as shown in the results.

The strongest association with recent temperature changes was observed in the concentrations of tree and weed pollens. For tree pollens, the association is positive with changes in temperatures in the same week (lag 0–1), whereas the association is negative with changes in temperatures in longer timeframes (lag 0–12 and 0–24). For weed pollens, the associations are positive for both immediate, seasonal and annual timeframes (lag 0–1, 0–4, 0–12, 0–52). Results in Supplementary Table S1 revealed that tree and weed pollens peak in Spring and Summer respectively. This suggests that for trees, their peak pollen concentrations are associated with rising Spring temperatures (likely associated with blooming season) and falling Winter temperatures. Similarly, for weeds, their peak pollen concentrations are associated with rising summer and spring temperatures.

Peak values of tree pollen concentrations were also associated with lagged values of precipitation (negative at lag 0–1 and positive at lag 0–4, 0–12, 0–24). This suggests that Winter rains are associated with increased tree pollen concentrations a few weeks later in Spring, but decreased tree pollen concentrations week immediately after. For details about individual tree, weed, grass, and mold species refer to Fig.  2 and Supplementary Tables S3 - S5 .

Mold concentrations were also observed to be significantly associated with lagged values of precipitations (lag 0–1, 0–4, 0–12, 0–24), suggesting that increased rainfall leads to increase in mold spores up to six months in the future. In the case of grasses, whose pollen concentrations peak in late Spring and early Summer, the association was found to be strongest with lagged values of temperature and precipitation from up to 6 months in the past (lag 0–24). This suggests that increase in Winter rain or decrease in Winter temperature are associated with higher grass pollen concentrations in the next season. Grass pollens were also observed to be negatively associated with lagged values of temperature from the previous year (lag 53–104) and positively associated with temperature of the same week. This suggests that increase in Summer temperature are associated with higher grass pollens in the same week.

In this dataset, strong associations between atmospheric CO 2 and pollen and mold counts were not observed. Previous studies also found it difficult to separate the influence of rising CO 2 from temperature change on growth or floral phenology of plants 28 . In our study, wildfire smoke exposure was also not found to be associated with pollen or mold concentrations for any of the major allergens.

In this retrospective analysis of pollen and mold concentrations in the San Francisco Bay Area during the past two decades, we observed that whereas average concentrations for most species is decreasing over time, the season length and number of active weeks are increasing. Further, these observations are statistically significant for the most commonly observed species and are also correlated with observed maximum temperature and precipitation in the region. While previous studies in this subject have looked at a limited number of species, our analysis covers more than twenty species observed in the studied region for a long time-period.

Some of our findings are consistent with the observations made in other studies. These include increasing pollen seasons, and their association with observed climate variables. However, we found that the average annual concentrations of most species in our study region has been decreasing over the years. Prior studies with regards to annual trends of pollen concentrations show a mixed result, with increases in some areas and decreases in other. Notably, a study of pollen counts in different areas in the United States 29 observed that the annual concentrations were increasing significantly in northern latitudes, but not in the southern latitudes. In our study, we observed increasing periods of activity for several species even as we observed a decrease in their average annual concentrations, suggesting that the pollen and mold activities are increasing outside their peak seasons. Rapid urbanization and land-use change could be a possible reason for decreasing trend of pollen concentration in the area under our study. Moreover, changes in climate variables like temperature could be due to both local change in land-use (e.g., urbanization) or global climate pattern. Both climate change and land-use change could bring about changes in the species of trees and plants in a region due to species migration or changes in architecture and landscaping preferences 28 .

While indoor molds are known to be present throughout the year, our study concerns outdoor molds, whose season peaks in Summer and Fall 30 and are known to cause allergic reactions. In the region of our study, we observed that mold species are the most commonly observed ones, and both the season length and number of active weeks for the most frequent among them have increased in the past two decades.

A major difference of our study in comparison to previous studies is the wide range of pollen and mold species covered in our analysis. Additionally, we also look at the changing trends for the number of active weeks of pollen and mold, in addition to their seasons. Seasons are the durations when pollen and mold concentrations reach their peaks. However, pollens and molds are active outside of those peak durations as well and knowing how these activities are changing could be beneficial to improve care for specific groups of people. Antihistamine and anti-inflammatory allergy medications can take up to 4 weeks to be fully effective 31 . Because individuals could be sensitivity to even small amounts of pollens and molds, our study could help both patients and physicians prepare ahead of peak seasons.

The relationship between climate change and phenology in a variety of plant species has been an area of increasing interest 22 , 32 . Previous studies have shown an advancement in the onset of pollen seasons in plants 33 , 34 . The U.S. Environmental Protection Agency has acknowledged the role of changing climate on pollen season 35 . A recent study using more than 20 years of airborne pollen data from across 13 countries in the Northern hemisphere demonstrated the effect of changing temperature on pollen season and load 28 . The International Phenological Gardens, a European network, has reported that since the 1960s, growing seasons have increased by approximately 11 days 20 . Ziello et al. reported an increase in atmospheric pollen of multiple types between 1977 and 2009 across Europe 36 .

Previous studies have shown that temperature and water availability correlate with pollen pro-duction intensity 37 , 38 . Increases in temperature directly increases pollen production both in the year prior to the pollen seasons, as well as in the month preceding flowering. A study from Spain examining the pollen trends of olive trees found increases in temperature were correlated with an earlier start and a later end to the pollen season each year between 1982 and 2011, demonstrating an increase in pollen production. Modeling suggested significant changes in the reproductive cycle of the olive tree due to climate change 33 . Several studies have demonstrated a relationship between higher temperatures and sun exposure the year prior to higher daily pollen concentrations the following year 39 , 40 . The previous summer’s temperature influences the intensity of pollen production as pollen grains are being formed the year prior, which depend on the photosynthates from the summer to reproduce in the spring. Studies have also found that higher temperatures in the month leading up to flowering also directly correlated with higher pollen concentrations 41 , 42 . Fungal spore concentrates increase with increased temperature 43 .

The relationship between rainfall, water availability and the concentration of pollen has been variable. Soil moisture is needed for seed germination but precipitation during flowering and pollen dispersal can wash out pollen and lower counts. Water deficits have been shown to delay olive flowering 44 , 45 . Drought conditions have been shown to decrease pollen in Switzerland and the Mediterranean 46 , 47 . In North America, tree pollen increases with increasing precipitation. However, Rasmusseen found that precipitation from the previous year was negatively correlated with average birch pollen concentration; although this was postulated to be due to a negative correlation between temperature and precipitation 45 . Increased water and soil moisture stimulate fungal growth spore growth and dissemination.

In our study, we also found significant associations of temperature and precipitation with pollen activities of multiple pollen species, consistent with prior work in this area. Additionally, this work sheds light into the role of changing climate with regard to individual species, as well as their short- and long-term influences (a few weeks to a year). Since different geographical areas have different prevalence of plant species that contribute to pollen activity, this analysis helps understand the unique characteristics of the San Francisco Bay Area’s pollen seasons and their changing nature.

CO 2 is the source of carbon for photosynthesis. Ziello et al. suggested that that rising CO 2 concentrations may be responsible for pollen increases 36 . Increases in CO 2 is also thought to contribute to mold growth. Zhang et al. used Bayesian modeling and found that annual mean CO 2 concentrations were significantly related to birch pollen levels and projected rising pollen counts in the next century 29 . Growth chamber experiments in which trees, grasses and weeds are exposed to higher levels of CO 2 show increase in pollen production 48 , 49 , 50 . Experiments have also shown that increasing CO 2 increases mold spore production 51 . However, it has also been noted that ascertaining the influence of rising carbon dioxide apart from temperature on pollen activity is hard to ascertain 28 . In our study, with regards to climate variables, as expected, we found that both CO 2 and maximum temperature shows statistically significant increasing trends. For the pollen and mold types we studied in the San Francisco Bay Area, we found that the annual average concentrations show a decreasing trend over the years with grass pollens and some frequently occurring molds and tree pollens showing statistically significant trends. For trees and several molds, the average number of active weeks shows a strong increasing trend over the years.

Future changes due to climate change are expected to further impact pollen production. Hamaoui-Laguel et al., using models to predict ragweed pollen concentrations in Europe found an anticipated four-fold increase in airborne pollen levels by 2050 52 , which has been predicted to increase rates of pollen sensitization 53 . Similar results have been found in Italy with increasing tree pollen counts and an associated increase in patients sensitized to pollen 54 . Better understanding the impact of climate change on pollen and mold spore production can guide predictive modeling to forecast pollen and mold production, improving public health measures to prevent asthma and allergy flares and prepare resources to respond to events that cause spikes in pollen and mold levels.

A limitation of this study was that we used a single site of pollen and mold collection and analysis. As pollen and mold spore concentrations are influenced by changes in the local environment and changes in landscaping, additional sites of collection would further strengthen the reliability of the data and interpretations. Thus, the results of this study provide insight into only the local region of the San Francisco Bay Area. The decreasing annual average concentrations for pollens and molds could be due to several of these reasons, including the rapid urbanization and change in vegetation cover in the area of our study. However, the findings are consistent with other studies examining phenology and climate change and suggest broad implications and a global impact of climate change on allergen activity.

Given the observational nature of the study, multiple environmental factors may be contributing to the observed findings. Given the complicated nature of plant biology, other factors are difficult to account for such as masting behavior, and the production of many seeds by a plant. Furthermore, local atmospheric changes and soil composition on pollen activity may have influenced our findings, but these variables could not be tested due to the lack of a suitable dataset. In addition to smoke exposure, particulate matter could also have influenced pollen activity and should be evaluated in future studies.

In future studies, we plan to examine the change in pollen concentrations and activities and their relationships with clinical outcomes. By combining datasets of electronic health records (EHRs), we could study how changing climate patterns and pollen activities affect patient visits as well as prescription of allergy medications. Additionally, datasets of land cover could be used to study the association between change in land-use with the changes in the activities and concentrations of pollens and molds. Although the most commonly observed species are specific to the study location, future studies could look into how the activities of some of the species observed in our study area have changed in other similar geographical locations across the world.

Extant research has largely focused on individual species or on a few taxa. We provide detailed analysis of pollen and mold activity for the twenty most frequent species in the area of our study, as well as for selected species of clinical significance. The long temporal span of this dataset (18 years) lends itself to studying the effect of changing climate on pollen and mold activity. As temperatures are increasing, the length of the pollen season for several species is significantly increasing. Similarly, there are strong associations between multiple pollen and mold species and climate variables, although for some species the direction of these association is not always uniform.

Collection and counts of pollen and mold spores

We used a database spanning 18 years (2002–2019) of weekly pollen and mold spore concentrations for an area in the San Francisco Bay Area (Los Altos Hills, Santa Clara County, CA, USA) obtained from a National Allergy Bureau (NAB) certified pollen counting station. The location of the pollen collection site and neighboring areas in the San Francisco Bay Area is shown in Supplementary Fig. S5 . Concentrations of outdoor pollens and mold spores were obtained with a Burkard Spore Tap (Burkard Collector) and were identified by species and also categorized as tree pollen, grass pollen, weed pollen or mold spore. The Burkard Collector is a volumetric air sampler and a standard device for monitoring airborne pollen and spores. This device draws in air at regular intervals and as a result, any airborne particles with enough inertia are captured on a surface inside the device, e.g., a greased tape or a microscopic slide. The capturing surface moves in a steady speed, allowing for newer samples to be collected. The device also has a wind vane and an ability to rotate, making it always oriented into the wind. The Burkard Collector can collect particles up to 3.7 µm and has been used in prior studies 55 .

Time Series Analysis (ARIMA).

ARIMA is a well-established method for time-series analysis and has been used to find associations between climate variables and health outcomes 56 . The pollen timeseries datasets have a seasonal component, as can be observed in the decomposed time series plots (Supplementary Figs. S6 - S9 ). For more details on time-series decomposition, see Supplementary Appendix Section “Time Series Decomposition.” For this reason, we used SARIMA, which is the seasonal variation of ARIMA, and which has the flexibility to control the seasonality and autocorrelation in the timeseries. In ARIMA( , , ) models, the target variable is predicted using three components: (1) past values (lags) of the target variable (AR or autoregressive), (2) differentiation of the timeseries, and (3) a moving average model (MA or moving average) on past forecast errors. The parameters for these three components together define the order of an ARIMA(p, d, q) model, where p, d, q correspond to the first, second, and third components, respectively. The seasonal ARIMA(p, d, q) (P, D, Q, m) model has an additional seasonal order where the parameters P, D, Q similarly refer to the seasonal variants of the first, second, and third components, and m refers to the frequency of the timeseries. This model is written in short as ARIMA(, , ) ( , , , ). All statistical analyses were performed in the Python programming environment (Python Software Foundation, http://www.python.org ) and p values < 0.05 were considered statistically significant. In all ARIMA models, the Box-Ljung test was used to test the null hypothesis that the autocorrelations of the residuals equal zero and the augmented Dickey–Fuller test was used test whether the timeseries was stationary.

First, univariate ARIMA( , , )( , , , ) models of different orders were fitted for the timeseries of pollen and spore concentrations of each major allergen (Trees, Weeds, Molds, Grasses) using the Box-Jenkins approach 57 . Additional information on species can be obtained from Tables S3 / S4 . The best performing ARIMA models for each allergen were chosen based on the Akaike Information Criterion (AIC), and they are presented in Table 4 .

Next, the best fitted ARIMA model was examined together with different climate variables. The statistical significance of the climate variables was then determined using these multivariate ARIMA models. Given prior finding in the literature than pollen activity can be influenced by climate factors from earlier seasons, climate variables at different lags (earlier periods) were included to check the associations of immediate, short-term, seasonal, and pre-seasonal climate variations with peak pollen and spore concentrations. The values of each climate variable were averaged for the following lagged durations: week 0–1 (immediate), week 0–4 (short-term), week 0–12 (seasonal), week 0–24 (pre-seasonal), week 0–52 (annual), week 53–104 (previous year).

Environmental data

Environmental data were collected from a variety of databases. These environmental variables and datasets have been used in prior studies on the environmental health 58 , 59 . The daily maximum temperature T MAX (measured in Fahrenheit) and precipitation data (measured in inch) were collected from the National Climatic Data Center of the National Oceanic and Atmospheric Administration (NCDC/NOAA). NCDC publishes historical climate observations for several monitoring sites across the United States. The San Jose monitoring site was selected because of its proximity to the site of the pollen and mold spore collection and as it had coverage spanning the period (2002–2019) during which the pollen and mold spore data were collected. For atmospheric CO 2 data, none of the monitoring sites in California had observations for the complete period (2002–2019); therefore, the CO 2 dataset (measured in parts per million) from Mauna Loa Observatory (MLO) of NOAA, located in Kona, Hawaii was used. This dataset informs us about the changes in CO 2 trends in the earth’s atmosphere. As a cross-check, we compared the correlation of the MLO dataset with the CO 2 observations during 2008–2017 from the Humboldt State University observatory in Northern California. We found a correlation coefficient of 0.85 for the 7-day moving averages in the two datasets. These datasets are overlaid in Supplementary Fig. S10 and the linear relationship between these two datasets is shown in Supplementary Fig. S11 , revealing a highly linear trend. For data on wildfire smoke exposure, we utilize the Hazard Mapping System (HMS) dataset developed by the National Oceanic and Atmospheric Administration (NOAA) of the United States government. On a daily basis, trained analysts use visible satellite imagery, satellite-based automatic fire detections, and infrared images to annotate fire locations and perimeter of smoke plumes 60 . Additionally, they also annotate the amount of smoke density (as low, medium, or high) and this dataset is available from 2010 onwards. From the daily dataset of smoke plume perimeters, we first identified smoke plumes that intersected with Santa Clara county. For those intersecting smoke plumes, we calculated the total area of smoke plume that lied wholly inside the county boundaries, resulting in a daily time series containing the area of smoke plumes that the county was exposed to.

Dataset preparation

The pollen and mold observations include weekly concentration of several commonly observed species in the collection area, although some weeks contain more than one observation. Those weeks with no pollen counts were treated as missing data. The pollen and mold observations were resampled to obtain a dataset with weekly concentrations. In addition, three datasets of pollen and mold spore concentrations were extracted from the raw observation files. The first dataset, called “Major allergens”, summarizes the concentrations for four major pollen and mold categories: trees, grasses, weeds, and molds. The second dataset (“Most-active species”) includes the concentrations for the twenty most active species. To identify the most-active species, the species were ordered by the number of total weeks in which each species had a concentration greater than zero during the complete observation period (2002–2019). Then, the top twenty species were selected from this list. The third dataset (“Selected species”) includes seven species which were picked based on their known importance in allergic outcomes 61 , 62 . Unlike pollen and mold concentrations which have a weekly frequency, the climate variables have a daily frequency. Moving seven-day averages of the climate observations were created to help offset the effect of short-term measurement effects and outliers, which is a standard practice in time-series analysis 63 . For smoke plumes we converted the daily timeseries to a weekly one by taking 7-day maximum area of smoke exposure. Finally, the weekly timeseries from the climate datasets were overlaid with the three pollen and mold spore datasets based on their dates. This generated combined time-series datasets of pollen and mold concentrations with corresponding climate variables. The annual average values for major allergens and different climate variables are plotted in Supplementary Figs. S1 and S2 .

Pollen species

We found over 100 different species of pollen and mold spores in our dataset, which are listed in Supplementary Table S5 . Since some species are observed more often than others, a list of 20 most commonly observed species was created. To create this list, each species was ordered by the number of weeks in which it had a concentration greater than zero. The list of 20 most commonly observed species is shown in Supplementary Table S4 . Similarly, owing to the clinical importance of some, a list of “selected species” was created containing Alternaria spp., Penicillium/Aspergillus , Quercus spp. (Oak), Cupressaeae spp. (incl. junipers/cedars), Betulaceae spp. (birch), Artemesia spp. (sage), and Ambrosia spp. /Franseria spp. (ragweed). Additionally, the counts for the four major pollen and mold were summarized as: trees, grasses, weeds, and molds.

Concentrations and activity for pollens and mold spores

Pollen or mold spore concentrations refer to the observations by the counting device during a given time period. When the concentrations are annually averaged, we call them annual average concentrations (AAC) and when they are weekly averaged, we call them weekly average concentrations (WAC). Seasonal and Annual Pollen or Spore integrals refer to sums of WAC values over a season (SPIn) and calendar year (APIn), respectively.

Further, we differentiate between weeks with pollen and mold spore concentrations greater than zero with those when the pollen and spore concentrations are zero. We refer to the weeks where the pollen and spore concentrations are greater than zero as active weeks and the total number of active weeks in a calendar year as Number of Active Weeks (NAW). In other words, active weeks correspond to duration, whereas integrals correspond to the quantitative extent of that activity. Finally, a pollen or mold season is the continuous period during a calendar year when their observations are most concentrated. Each season has a starting week and an ending week, and the season length refers to the encompassing number of weeks. To calculate season length, we followed the procedure described in Ziska et al. 28 . To identify the start of the season, we take the first continuous 4-week period of the year when the concentrations are greater than zero and take the last week of that 4-week period. To identify the end of the season, we take the last continuous 4-week period of the year when the concentrations are greater than zero and take the last week of that 4-week period. For some species on some years, there were no continuous 4-week period with concentrations greater than zero. In those cases, we took a second approach and considered the fourth week when the concentrations are greater than zero as the start of the season and fourth-from-the-end week when the concentrations are greater than zero as the end of the season. Even after this procedure, for some species on some years, we observed less than 4 weeks when the concentrations are greater than zero. For those, we took a third approach and considered the first week when the concentrations are greater than zero as the start of the season and the last week when the concentrations are greater than zero as the end of the season. In Figs.  1 – 2 and Supplementary Fig. S4 , only those species for which we could calculate the season using first or second approach for at least 10 years are shown.

Consider the following example to illustrate the differences between these measures. If in a given year pollen concentrations are greater than zero on weeks 8, 15, 16, 17, 18, 20, 22, 25, 26, 27, 28, 35, the value of NAW is 12. The value of APIn is the sum of pollen concentration on all of these 12 weeks and the AAC is the average of these values. The season starts on week 18, ends on week 28, and the season length is 10 weeks. The value of SPIn is the sum of pollen concentrations from week 18 to week 28.

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These authors jointly supervised this work: Mary Prunicki and Kari C. Nadeau.

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Sean N. Parker Center for Allergy and Asthma Research, Stanford University School of Medicine and Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, Stanford University School of Medicine, Stanford, CA, 94305, USA

Bibek Paudel, Meng Chen, Vanitha Sampath, Mary Prunicki & Kari C. Nadeau

Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, 94305, USA

Theodore Chu

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B.P. was responsible for statistical methods, study design, data analysis, writing; T.C.: collected the data; MC was involved in study design, writing, data interpretation; V.S. developed the manuscript; MP developed the manuscript; K.N. was responsible for leading the project, study design and data interpretation.

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Correspondence to Kari C. Nadeau .

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Paudel, B., Chu, T., Chen, M. et al. Increased duration of pollen and mold exposure are linked to climate change. Sci Rep 11 , 12816 (2021). https://doi.org/10.1038/s41598-021-92178-z

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Science project, how does mold grow.

Mold is a fungus that needs nutrients and water to grow. Mold can be found indoors and outdoors all over the world. Most are non-toxic, but they certainly aren't good to eat!

Mold can grow on surfaces like rocks and walls, but in homes it commonly grows on aging food. Many foods, especially bread, contain mold inhibitors and preservatives to prevent mold from growing quickly.

Which food will grow the most mold? The least? Why? Which environment has the greatest mold growth?

• Plastic zip-top bags
• Labeling tape and marker
• Two or three types of food (such as greens, bread, meat, cheese, fruit, etc.)
• Notebook and pen or pencil
• Spray bottle
• Cooking pan, toaster oven, oven or other cooking device.
• Camera (optional)
• Select some different foods to test.
• Have an adult help you cut your samples. You will need 9 samples for each type of food.
• Take 3 samples of each type of food and cook them. How might this condition affect how mold grows on the food?
• Place each sample into a plastic zip-top bag and seal it. Label each bag appropriately with type of food, the conditions, and environment.
• Take 3 samples of each type of food and spray lightly with water. Do you think the wet samples will grow mold more quickly or slowly? Why?
• Take the last 3 samples and place each sample into a plastic zip-top bag and seal it. Label each bag appropriately with type of food and environment.
• Place one cooked, one wet, and one dry set of samples for each type of food in the refrigerator.
• Place one cooked, one wet, and one dry set of samples for each type of food in a dark place like a cupboard.
• Place one cooked, one wet, and one dry set of samples for each type of food outside in a sunny, warm spot.
• Monitor your samples daily and make notes on observations. Taking pictures is a great way to track changes in your samples over time.

Wet samples will grow the most mold, while cooked samples will grow the least mold. Samples left in the sun will grow the most mold, while refrigerated samples will grow the least mold.

Molds need water and nutrients to grow, so wet, uncooked samples will provide the most nourishment to many types of molds. Cooking food often denatures (destroys) many proteins and nutrients in food and makes it harder for mold to use the nutrients for growth.

Mold also thrives in warm environments, so the samples left in the sun will mold first. Refrigeration prevents cell activity in many living things like fungi and bacteria, which is why foods typically last longer in the refrigerator.

We may not want to eat mold, but mold can be very useful! Many kinds of mold are used to produce life-saving medicines, or clean up toxic oil spills. They are great for many biological and engineering purposes because they are simple and reproduce quickly.

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Mold is in the Air

What is mold.

Mold is a type of fungus. The tiny cells of mold are called spores. Mold spores live in the air all the time—there are millions of them practically everywhere.

But when the mold spores land on a host, they grow and thrive by feeding off the food they land on. Mold spores feed themselves by producing chemicals that break the composition of the food down so the spores can grow while the food rots away.

Is mold bad or dangerous

It is not safe to eat mold.

It is not safe to breathe mold.

Even mold is useful

Here is what you need:, here is what you do:, here is what happened:.

Foods with lots of preservatives and chemicals in them do not usually mold. They don’t mold because the preservatives in the food kill the mold spores before they can start growing.

The results of this experiment will be somewhat different if you vary the temperatures of the places you put the bags. Put some at room temperature, some in a warm, dark place (like a closet), some in the refrigerator, and some in a sunny window sill.

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How to Remove Mold from Shower Caulking

Keep every inch of your shower squeaky clean with this mold removal and prevention guide.

Patrick Biller

Due to high humidity levels, mold can sneakily build up in bathroom corners and crevices. Porous surfaces in the shower, such as grout and caulking, are especially vulnerable to mold and mildew growth . Caulking is a mold magnet even though its purpose is to be a moisture sealant. If it wears down or cracks over time—or if it was improperly installed to begin with—it loses its ability to be waterproof.

The good news is that it’s a relatively easy fix. As with cleaning grout , removing mold requires just a handful of household ingredients. Learn how to remove mold from your shower caulking (or replace it if necessary) and see how to prevent it from accumulating in the first place.

What Causes Mold to Grow in the Shower?

Mold has the potential to pop up anywhere in your home that has high levels of humidity and moisture. So it’s no wonder that bathrooms, and the showers and tubs within them, are susceptible to mold growth. In the case of caulking, there are several factors to consider.

Other than its repeated exposure to water when the shower is in use, moisture can collect onto caulking and linger long after you’ve turned the faucet off. Soap scum and other residue (both from your body and the products you use to clean it) may also stick to caulking and act as food for mold. If you notice gaps in the caulking or if it’s begun to peel away from the tile edges, there’s a good chance mold is hanging out just under the surface (if it hasn’t seeped through already). Although it’s unlikely, there is the possibility that standard caulk (which is not moisture- and mold-resistant) was used when sealing the shower. If you know for sure that it was or even suspect it, consider swapping it out for mold-resistant caulk using our tips below.

TRIA GIOVAN

There are two easy solutions to kick caulking mold to the curb, but, as always, safety comes first. Before attempting either method, ensure the bathroom is adequately ventilated by turning on the exhaust fan and, if available, opening a window. Consider wearing rubber gloves, especially when using bleach. Also, never attempt to combine the two methods, which use vinegar and bleach, respectively, as mixing the two chemicals will release toxic fumes that can be dangerous.

Method 1: Remove Mold with Vinegar

While vinegar isn’t ideal to use on unsealed grout, it’s safe and effective on silicone caulking. It’s also one of the most successful (and all-natural!) ways to combat mold. Simply fill a spray bottle with white vinegar and generously apply it to the caulking where mold appears (being careful not to get too close to any surrounding unsealed grout). Leave the vinegar application for at least one hour, allowing it to kill spores. Then, go in with a small, soft brush ( an old toothbrush can do the trick !) and scrub until the mold disappears. Rinse the caulking and then wipe it completely dry using a clean cloth.

Method 2: Remove Mold with Bleach

For more pervasive or stubborn stains on shower caulking, bleach can serve as an extra powerful mold killer. Dilute bleach with water in a spray bottle and use it to saturate the moldy spots along the caulking. Let it sit for approximately thirty minutes before following up with the same scrubbing, rinsing, and wiping process as you would with vinegar. If mold persists, with either the bleach or vinegar methods, repeat the process (but remember not to try one after the other without completely removing the previous chemical and giving the bathroom time to air out).

Method 3: Replace the Caulking

Once shower caulking begins to show wear and tear, or if it was poorly applied from the start, it’s nearly impossible to prevent mold from growing. Even if you regularly clean visible mold and mildew on the outside of the caulking, you can still be breathing in the invisible spores. The best thing to do in this case is completely replace it, but, fortunately, it’s a simple and inexpensive project.

First, remove the old caulk and thoroughly clean the area underneath, using either vinegar or bleach. Once it’s dry, use a caulk gun to apply new mold-resistant silicone caulk along all the edges of the shower. While most caulk will dry in under two hours, it can take up to two days to fully cure, which is vital if you want it to be waterproof (which you do). Keep that in mind when planning this project, especially if you’re working on your home’s one and only shower.

How to Prevent Mold in the Shower

To minimize the amount of mold growth and the time spent cleaning it, make the following habits part of your daily bathroom routine.

• Keep the shower dry when not in use: Remove excess water by wiping the walls with a squeegee or a towel, paying extra attention to areas with caulking, after every shower.
• Maintain appropriate ventilation and humidity levels in the bathroom: Check to ensure fans are working properly , and always run them when showering. If your bathroom gets excessively humid (and you don’t want to give up your steamy hot showers), consider cracking a window or adding a dehumidifier .
• Clean the shower routinely: Sticking to a regular bathroom cleaning schedule will help fend off mold buildup by tackling the residue that feeds it. Furthermore, cleaning the shower often provides the opportunity to inspect caulking for cracks. Catching them quickly may make the difference between repairing small areas of damage as opposed to replacing the entire caulking.

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