activity

All those holes inside a soft, chewy loaf of bread are the handiwork of microscopic (really tiny) yeast! Find out what temperature yeast likes best in this bubbly experiment.

safety
  • Uses the microwave
difficulty
  • Beginner
time
  • 30 minutes, plus 1 to 1½ hours rising time

hey curious cook—

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Prepare Ingredients

Ice
Water
1½ teaspoons
instant or rapid-rise yeast
1½ teaspoons
sugar

Gather Equipment

Large glass
Marker
3
snack-size zipper-lock bags
½-teaspoon measuring spoon
1-tablespoon measuring spoon
Rimmed baking sheet
Small microwave-safe bowl
Oven mitts
Fine-mesh strainer
1
 
Ice
Water

Fill large glass with ice and water. Set aside.

 
2
 

Use marker to label 1 zipper-lock bag “Cold,” second bag “Room Temperature,” and third bag “Hot.”

 
3
 
1½ teaspoons
instant or rapid-rise yeast
1½ teaspoons
sugar

Add ½ teaspoon yeast to each bag. Then, add ½ teaspoon sugar to each bag.

 
4
 

Add 2 tablespoons room-temperature water to bag labeled “Room Temperature.” Seal bag, squeezing out as much air as possible. Place bag in center of rimmed baking sheet.

 
5
 

Fill small bowl about halfway with water. Heat water in microwave until steaming, 30 seconds to 1 minute. Use oven mitts to remove bowl from microwave. Add 2 tablespoons hot water to bag labeled “Hot” (ask an adult for help). Seal bag, squeezing out as much air as possible. Place bag on right side of baking sheet. Discard remaining hot water.

 
6
 

Hold fine-mesh strainer over now-empty small bowl. Pour ice water through fine-mesh strainer. Discard ice. Add 2 tablespoons ice water to bag labeled “Cold.” Seal bag, squeezing out as much air as possible. Place bag on left side of baking sheet.

 
7
 

Set baking sheet aside in a place where it won’t be disturbed. Make a prediction: At which temperature do you think the yeast will be the MOST active (make the most carbon dioxide gas)? Why do you think so?

 
8
 

After 1 to 1½ hours, observe your experiment. Which bag inflated the most? Those yeast were the MOST active. Which bag is the flattest? Those yeast were the LEAST active. Check out “Food for Thought” to learn why it’s important to let yeast doughs rise at just the right temperature.