Moldy Bread Experiment – What Makes Mold Grow?

This fun and educational moldy bread experiment will show you what factors influence mold growth and how to prevent it. It’s a perfect project for science fairs!

Moldy Bread Science Fair Project

Are you tired of throwing out food that has gone moldy far before its expiration date? Ever been curious about what causes bread to spoil so quickly? 

If so, then this moldy bread experiment is perfect for you! You will have so much fun investigating the effects of humidity and temperature on mold growth with your kids. And while the fuzzy mold is a bit disgusting, it is contained in plastic bags so you don’t need to worry about touching or breathing in mold.     

This molding bread science experiment will take several days, so make sure you leave plenty of time for the science project. Your kids will get to observe the stages of mold growth up close and find the conditions in which you should store your bread at home.

What is Mold?

Mold is an unwelcome house guest, often found lurking in dark and damp areas. But did you know it’s actually made up of tiny organisms called hyphae and spores that work together to form colonies? Chances are this hidden fungus can be sneaking around inside your home or even on the food products you buy – so watch out!

The presence of mold on bread is caused by various factors including lack of hygiene practices in the kitchen; the use of old or stale bread; improper storage either at home or in commercial bakeries; high humidity levels; and insufficient sunlight exposure.

Different types of mold can be found on bread. Some include Penicillium (blue-green), Aspergillus (gray-green), and Alternaria (dark green). These molds occur when moisture is present in the environment along with warm temperatures. Bread that has been stored for too long or not packaged properly is most likely to suffer from mold growth.

How to Perform the Moldy Bread Experiment

There are many ways to perform the moldy bread science experiment. It all depends on what you want to test! 

Here are several ideas for your experiment:

  • Sunny vs. dark
  • Dry vs. wet
  • Cold vs. warm
  • Preservatives vs. no preservatives
  • Open bag vs. closed bag
  • Paper bag vs. plastic bag

After you decide what conditions to test, have your kid form a hypothesis as part of the scientific method. To form a hypothesis, your kid needs to think about what he or she thinks will happen to the bread. For example, the hypothesis could be “I think the bread will grow mold faster in a dark and wet environment.”

In our moldy bread experiment, we decided to test what happens to the bread in a dark vs. sunny, wet vs. dry, and cold vs. warm environment. These are the typical environments we expose our bread from the grocery store to, so we wanted to know what factors influence mold growth on bread so that we can extend the shelf-life of our bread.


  • 6 slices of bread (any type will be fine as long as they are all from the same loaf) 
  • Resealable bags
  • Sticky notes 
  • Pen or pencil (you can also use a permanent marker and write directly on the bags)


1. Place a slice of bread in each resealable bag.

2. Label each bag with the conditions you are subjecting the slice of bread to. Some people skip this step, but I believe it is crucial to label all the bags accordingly to avoid confusion in the observation step.

Moldy Bread Experiment Dry Bread Slices

3. Prepare the bread slices. We sprayed 3 of the bread pieces with some water.

Moldy Bread Experiment Wet Bread Slices

4. Place the bags in the appropriate areas of the house. We put a couple of bread slices near the window to get sun exposure. We placed a couple in the kitchen cabinets to keep them in the dark. And we placed a couple in the fridge to see how the temperature would affect the mold growth on the bread.

5. Leave the bread alone to allow mold to grow! Since we used store-bought bread with preservatives, it took a few days before any mold showed up. If you want the results faster, I recommend buying bread without preservatives. 

Molding Bread Science Experiment Results

After about a week, we put all the bread slices side by side for comparison.

Moldy Bread Science Experiment Results

Not surprisingly, the bread that was wet and stored in a dark environment had the most mold growth. In fact, the mold growth was drastically more than the other bread pieces, and pretty disgusting if you ask me! 

Moldy Bread Experiment Wet and Dark Slice

Upon close observation, there appeared to be 3 types of mold growth on the “wet and dark” slice. You can see a gray-green mold, white mold, and also yellow mold. 

Moldy Bread Experiment Fuzzy Mold

The wet and sunny bread slice had some black and fuzzy mold growing on it. You could see the mold growing out from the edge of the bread piece. Yuck!

Then we looked at two bread slices that had one common environmental factor side by side for comparison. 

Comparison 1: “Wet & Sunny” vs. “Wet & Dark”:

Moldy Bread Experiment Wet and Dark Slice

While both bread slices had mold growth, the one in the kitchen cabinet had a lot more. Therefore, the sunlight had an effect on preventing mold growth.

Comparison 2: “Dry & Sunny” vs. “Dry & Dark”:

Moldy Bread Experiment Both Dry Slices

My personal hypothesis was that keeping the bread slices dry would prevent mold growth, but I was wrong! Both of these slices of bread were kept dry but the one in the dark had significant mold growth. 

There was a little bit of mold growth on the bread piece left out in the sun, but not much.

In combination with comparison 1, the results suggested that molds thrive and grow better in dark environments.

Comparison 3: “Dry & Fridge” vs. “Wet & Fridge”:

Moldy Bread Experiment Cool Temperature Bread Slices

Both bread slices were mold-free (at least as far as we could see), even though one of them was wet. It would appear that placing the bread in the fridge and subjecting it to a cold temperature effectively prevented mold growth.

The question was whether the cold temperature or the light was more effective in preventing mold growth on bread. So let’s look at the bread slices that were both exposed to sunlight.

Comparison 4: “Dry & Sunny” vs. “Wet & Sunny”:

Moldy Bread Experiment with Light

Even though we learned that the bread pieces exposed to sunlight had less mold than the ones placed in a dark environment, sunlight still did not completely prevent mold growth. We could still see a decent amount of mold on the wet slice of bread, and minimal mold growth on the one we kept dry.

Comparison 5: “Dry & Dark” vs “Wet & Dark”

Moldy Bread Experiment Dark Environment Comparison

From the above comparisons, we had already seen that light is a major factor in preventing mold growth on bread. When you compare the dry and wet slices that were both placed in the kitchen cabinets, you could see that both had a lot of mold growth.

The wet bread slice had much more mold growth than the piece that was kept dry.

Moldy Bread Science Project Conclusion

From the comparisons, there was much to observe and analyze in this experiment. Then combining all the observations, you could draw a conclusion on how to prevent mold growth. That’s why the moldy bread experiment is a great science project for the science fair.

Growing mold on bread is also a great experiment to help the kids walk through the scientific method.

And finally, what did we conclude from the moldy bread experiment? That we should store bread in the fridge when possible. If not, keep the loaf of bread dry and in a place that has light!

There are so many other things you can test on the bread slices. For example, we can take this science experiment one step further and see if light from the sun affects mold growth differently than light from a lightbulb. Or even test different types of lightbulbs!


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