Kids, did you make your own yeast according to last month¹s column? It is really fun chemistry to do hands-on and it has a biological slant (in a word, "biochemistry"), so we hope that you did. If you had to refrigerate your starter yeast in order to wait for this column to appear, remove one cup of it and feed it for a few days, twice a day, as you did on days 11-14 before. Now you are ready to start a "Sweet Friendship Bread". In a glass bowl mix 1 cup each starter, vegetable oil, and sugar, 4 eggs, and 2 tsp vanilla. In another large glass bowl mix 2 tsp baking soda, 1 tsp baking powder, 2 cups flour, 2 tsp cinnamon, and 1 cup each chopped pecans, chopped apples, and raisins. Blend every-thing, mix well, and pour into three 9x5" loaf pans. Have an adult partner bake it for 50-60 min in a preheated 350^oF oven.

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

Yeast cells digest food to grow. Their favorite food is sugar, either sucrose (cane sugar), fructose and glucose (from honey, molasses, and fruit) and maltose (from starch in flour). Glucose is C₆H₁₂O₆. This fermentation process makes carbon dioxide and ethyl alcohol. Flour Facts: When mixed with liquid and kneaded, flour develops enough gluten to support the carbon dioxide made by the yeast. Gluten is the elastic molecule formed when the protein of flour meets a liquid. Kneading makes the gluten stronger so it can hold in the gases formed by the yeast. This recipe didn¹t call for kneading, but many do. After baking the dough you¹ll see the remains of the CO₂ gas bubbles as air pockets in the bread. Fat Fact: Fats like butter, margarine, and oil are used in breads to make the gluten strands slippery so the yeast gases can expand easier. Liquid Facts: Breads made with water will have a more open texture, a more wheaty flavor, and a crispier crust. Milk creates breads that are richer with softer texture; crusts are softer and will brown faster due to the sugar and butterfat in milk. Sugar Facts: Sugar provides food for the yeast to grow and adds flavor. Salt Fact: Salt controls the speed at which the dough rises. In next month¹s column we¹ll do more experiments with yeast, so stay tuned!

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Kathleen Carrado Gregar, PhD, Argonne National Labs 
[email protected]
January 2001

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Reference: Nancy Lang, Scientific American Explorations magazine, Fall 2000, p. 14 and www.redstaryeast.net/science.htm.   See www.breadworld.com/justkids for a peanut butter bread recipe with Fleischmann¹s yeast.