Bread Mold Experiment

Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Imagine you walk into the kitchen and notice the dreaded sight of moldy bread. Have you ever wondered why mold can grow on bread? In this lab, you will discover how light and temperature influence bread mold growth.


Research question How fast does mold grow in light/dark and cold/warm environments?
Age Middle school and up
Time to complete 10 days
Safety concerns Some people can be allergic to mold. If that is the case, do not perform this experiment. Wear gloves and a mask, and do not eat or drink when working with the moldy bread. Don't forget to wash your hands!
Independent variable Time, light and temperature
Dependent variable Rate of mold growth
Controlled variables Bread thickness and size

Have you ever thrown away moldy bread in your house? Was it decorated with spots of green and white or fully covered in mold? Those spots are actually microscopic organisms called mold. A type of fungus, mold can be found just about anywhere from our door knobs and damp clothing to bread! To learn more about the science behind mold check out this lesson: What is mold?

Bread that has mold growing on it
moldy bread

Does mold on bread grow faster in different environments? To answer this question, we will monitor how fast mold grows in each of these environments:

  • Sample #1 - Dark
  • Sample #2 - Light
  • Sample #3 - Cold
  • Sample #4 - Warm

Depending on how much mold we see over a period of time, we can graph the rate at which mold grows. Rate is equal to the amount of mold growing over time.


  • 4 slices of bread from a loaf of bread (any brand will do)
  • Four plastic bags
  • Permanent marker
  • Small lamp
  • Dark box
  • Lab notebook that has the following observation table and data table:

Observation table:

Condition Light Dark Cold Warm
Grew mold

What mold looked like?

Day of first growth

Data table:

Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 Day 9 Day 10


1. Take your plastic bag and label each as sample 1 - 4 on the bag in the upper right hand corner.

2. Draw a grid on the plastic bag that has a total of 10 boxes. Try to get make your grid the same size as the slice of bread.

3. Insert a slice of bread in each of the labeled plastic bags and tightly close the bags.

4. Place sample #1 in your dark box, sample #2 under a light that you will be keeping on throughout the experiment, sample #3 in your refrigerator and sample #4 on top of your refrigerator.

5. Each day, examine your four samples and write down how many boxes in your grid have mold. Make note of any changes using your tables in your lab notebook.

6. After 10 days, stop the experiment and begin your data analysis.

7. Data analysis:

Let's create a rate graph using your data table. The x-axis will be labeled 'mold growth.' This is the dependent variable or total number of boxes you counted for each day. The y-axis will be labeled 'time,' which is your independent variable. Your final graph should resemble a line graph. Be sure to complete this step for each sample.

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