Help your young scientist explore yeast in action during this simple experiment you can do on the kitchen counter. Click on the below links to print off your (free) experiment!
What is yeast? Why is it added to bread?
Yeast is a micro-organism (micro = tiny, organism = living thing) that can be found all around us. There are many different kinds of yeasts. Some naturally-occurring yeast can be found on our skin. Other naturally-occurring yeasts can be found on the skins of fruits and vegetables. Some yeasts are used to make industrial products like ethanol (which is used as fuel to make cars run).
However, many of us are most familiar with the type of yeast we use to make bread. The scientific name of this type of yeast is Saccharomyces cerevisiae. Baking yeast can be found in the grocery store under names like: “active yeast,” or “instant yeast,” and can be found in packets or jars. Most of us home cooks are familiar with yeast that takes the form of dehydrated granules (your young scientist may think the granules look like sand).
Yeast is fed with a sweetener, like sugar or honey. When the yeast eats sugar, carbon dioxide gas is produced and little bubbles get trapped in the bread. It’s important that the carbon dioxide gas is produced gradually, and not all at once. The gradual process allows the bread to rise, and makes bread fluffy inside. (The gluten network in bread dough also helps contribute to the rise. Air bubbles get trapped the gluten, leaving a nicely leavened loaf.)
When the loaf of bread is baked, the heat ends up killing the yeast. However, the gas bubbles that were trapped in the loaf can enlarge during baking as the entrapped air can expand, and water converts to steam.
- 1 small, clean, empty bottle with a neck (A clear pop bottle works great. Make sure the bottle is large enough that the water only fills it 2/3 full. )
- 1 cup warm water, not too hot or cold! (Try to get water 100-110F)
- 2 packets of quick rise instant yeast
- 2 tsp. sugar
- 1 latex glove, or balloon
- 1 rubber band
- Clock or stopwatch
- Add warm water to clean, empty bottle. Explain to your scientist that the water must be the right temperature so the yeast is not too hot or too cold. Yeast activates in temperatures approx. 100-110F.
- Sprinkle yeast into water/sugar mixture and stir. Explain to your scientist that the yeast is inactive, or “sleeping.” Let them observe the yeast before adding it to the water.
- Sprinkle sugar into water, and stir to dissolve. Explain to your scientist that the sugar will “feed” the yeast.
- Immediately cover the top of the bottle with the glove so the opening of the glove is fastened over the opening of the bottle, fingers pointing up. Rubber band the glove tightly to the bottle. Explain to your scientist that you’re going to watch what happens to the glove.
- What do you observe about the experiment? Is the glove flat, or inflated?
- How long does it take the glove to inflate?
Discuss with your scientist what they see, hear, smell, etc. All observations are important!
- Why did the glove inflate?
Discuss with your scientist how the yeast made a gas (carbon dioxide), which blew up the glove just like a balloon. Review what was learned during the experiment.
Miss the free download? Scroll up to the top, click the link for the student-led experiment and/or teaching guide, and print!