Butch Piccolo, age 12, of Spokane, Wash., for his question:
HOW DOES YEAST MAKE BREAD RISE?
The first bread was made ages ago, before the dawn of history. It was flat and heavy and most likely hard to digest. We get the same sort of loaves today when we forget to add yeast or fail to provide the right conditions for the yeast to thrive and multiply. The doughy mixture must be moist and warmish and contain suitable nutrients. It also must be left awhile to do its work in peace and quiet.
The best bread is homemade, and anybody can lend a hand. This is nice because the project is fun and the rewards are fantastic. The fragrance and the flavor are unforgettable. When you use natural grains and wholesome ingredients, every bite adds a boost to the diet. Try a recipe sometime. The job calls for a few spurts of muscular mixing and whacking, separated by lazy rest periods.
The important work is done by the yeast, which makes the dough rise by filling it with spongy little bubbles. Yeast is a multitude of mini single cell plants, related to mushrooms. While in their package, they rest in a dormant state. When well mixed into the dough, they come to life. The doughy mixture provides food. Warmth and moisture provide the right conditions to thrive and multiply.
The ingestion of food, even in simple plants, is a complex process of reassembling chemicals and separating the useful ones from the wastes. As it thrives, the yeast produces enzymes that make sugar and starch ingredients more digestible. Diatase breaks down starches; invertase changes one sugar to another; zymase breaks down sugars.
Naturally this fantastic chemical activity produces waste products. These include alcohol and carbon dioxide. The gaseous carbon dioxide collects in small bubbles, trapped within the tacky dough. As the bubbles multiply, the spongy dough begins to rise.
To perform this miracle, the yeasty dough must be leftin peace for an hour or so. It must be warm because the sugar¬changing activity needs temperatures between 80 and 85 degrees. The rising bread doubles in size. Then we punch it down and give it another hour or so to double its size again. The light, spongy dough is now ready to shape into loaves and bake in the oven.
The finished loaf does not contain the waste alcohol. This chemical disappears in the hot oven. The yeast cells are destroyed, adding their rich proteins to the bread. The heat dries the moist dough which sets around the gassy bubbles, making the loaf light and spongy. Try to let it rest a little while before you slice it, or some of the spongy bubbles may go flat.