Can a tiny packet of yeast inflate a sealed plastic bag? Yeast cells are living organisms that eat sugar and release carbon dioxide gas. That gas is what makes bread dough rise.
You dissolve one packet of rapid-rise yeast in a cup of lukewarm water. You stir in half a cup of sugar. Then you pour the mixture into a large freezer bag and seal it tightly. After about an hour in a warm spot you check the bag.
The bag puffs up with carbon dioxide. Each yeast cell can process roughly its own weight in sugar per hour. Billions of cells working together produce enough gas to see and feel.
Hypothesis
The hypothesis is that yeast produces carbon dioxide gas, which makes bread rise and gives it a fluffy texture.
Yeast cells are living organisms that eat sugar and release carbon dioxide gas — the same gas that makes bread dough rise. You dissolve a packet of rapid-rise yeast in lukewarm water, stir in half a cup of sugar, and pour the mixture into a large freezer bag sealed tightly. After about an hour in a warm spot, the bag puffs up. Billions of cells working together produce enough gas to see and feel.
Yeast cells eat sugar and release carbon dioxide gas. Billions of cells working together produce enough gas to inflate a sealed bag. That same gas is what makes bread dough rise.
Ethanol is a type of alcohol that yeast makes when it breaks down sugar. You mix lukewarm water, sugar, and yeast in a plastic bag. The yeast cells eat the sugar and release gas as they produce ethanol.
Glucose is a simple sugar that cells use as their main source of energy. This project uses half a cup of sugar and yeast in a plastic bag. The yeast cells use that sugar for energy and release carbon dioxide gas.
Method & Materials
You will mix lukewarm water, sugar, and yeast in a plastic bag, then put it in a warm place.
You will need one large Ziploc-type freezer bag, one envelope of "rapid-rise, active, dry yeast", 1 cup lukewarm water, and 1/2 cup sugar.
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After an hour, you will see that the bag has partially filled with gas, and that the liquid is full of carbon dioxide bubbles that the yeast has produced. You may even see a noticeable amount of puffiness in the bag after two hours.
Why do this project?
This science project is interesting because it shows how a tiny organism like yeast can have a big impact on the texture of bread.
Also Consider
Experiment variations to consider include using different types of yeast, different temperatures of water, and different amounts of sugar.
Full project details
Additional information and source material for this project are available below.
