Yeast Fermentation Science Projects for Third-Graders

Cheap, safe, readily accessible and fast growing, yeast is the perfect living creature to research for a science project. Fermentation is the process in which yeast converts sugar into alcohol and carbon dioxide. Yeast needs water, nutrients, a warm temperature and oxygen. Altering the quantity or qualities of yeast's basic needs is a great way to start a science project. There are also ways to slow the growth and fermentation of yeast, including changing the pH, or adding salt or another preservative.

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Start with a 1-to-1 ratio of food to dried yeast. For example, use 2 teaspoons of sugar to feed 2 teaspoons of yeast. For every teaspoon of yeast, use 4 tablespoons of water. Yeast is greatly effected by temperature. Too hot and it will die, too cold and it will not grow. The best temperature is within 70 to 80 degrees Fahrenheit. To use a different unit of measurement such as Celsius instead of Fahrenheit or milliliters instead of tablespoons, you can use an online converter such as ConvertMe.com.

Whichever variable seems most interesting to you is the best one to study, but only change one variable at a time so you can tell exactly what caused the changes you will see. If you want to study the effect of temperature, only change the temperature of the water -- keep the food, amount of yeast and water the same. If you want to measure how the food supply affects fermentation, you can add different amounts of sugar or use different foods such as flour, cornstarch, artificial sweeteners or whatever you choose, but keep the temperature, amount of yeast and water constant. You can also alter the amount of yeast or water or add another ingredient such as salt, lemon juice or baking soda to test whether it affects fermentation.

Once you have decided which variable to study, determine how to measure the rate of fermentation. As fermentation releases carbon dioxide bubbles, you can measure the gas produced. One possibility is to mix the dry ingredients in a plastic bag, add the water, then seal the bag. Compare how fast or how much the bag gets filled with carbon dioxide. You could also complete the experiment in soda bottles, putting a balloon over the opening. As fermentation occurs, carbon dioxide will fill up the balloon.

Yeast loves sugar and starch, two ingredients in bread. As it eats, fermentation releases gas bubbles, which makes the bread rise. The bubbles pop, but holes in the bread are evidence that they were there. To experiment, first follow the bread machine directions exactly as written. Then begin to change one variable at a time by adding more or less of the ingredients. You can also change the sweetener -- sugar, honey, artificial sweetener or natural sugar; change the type of flour; the temperature or the amount of salt or lemon juice. Compare the breads for their density, taste and size.