Bread Bag Nightmares - 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 this stuff 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, come back to this page to test your newfound knowledge by answering the questions below. (No fair peeking at the answers before you do the activity!)

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

dripbread2. 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!

breadgraph5. 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.



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

This experiment is based on an activity developed by the National Association of Biology Teachers.



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