Robyn Diehl.. age 12, of Phoenix. Ariz., for the questions
How does yeast make bread rise?
Without yeast, our bread would be flatter then pancakes, heavy and hard to digest, The basic ingredients of bread are flour and water, A little yeast and a little time turn this doughy mass into spongy loaves. The work is done by tiny single plants and all they do is eat and multiply. In the process, they give off quantities of carbon dioxide gas which fill heavy dough with small pockets end bubbles.
A spoonful of yeast is actually a colony of countless fungus plants small cousins of the mushrooms and larger cousins of the bacteria. Most yeast cells are egg shaped, equally round at each and. Some are round as globes and some are long and sausage shaped, The bread making yeasts are usually oval in shape.
Yeast cells are so small that we have to study them under a microscope; If we could make a row of them lengthwise, it would take about 3,000 of them to measure one inch. In width, they measure about 5,000 to an inch. The main difference between the yeasts and their smaller bacteria cousins is in the way they multiply. Bacteria multiply by dividing in two. Each tiny cell becomes twins, leaving no parents or grandparents,
A single yeast cell multiplies by budding. If conditions are good the parent cell begins to sprout a small bud. In half an hour, the bud is half as big as its parent. In one hour, the mother and daugh#er cell are equal in size. If conditions continue to be good, both mother and daughter begin to sprout a bud apiece.
In two hours, the mother cell has two daughters and a granddaughter. Each cell is then ready to sprout another bud as a rule, the younger cells remain linked to the older generations and the yeast colony grows in long chains of cells.
Conditions are good when there is warmth, moisture and plenty of food. To remain active, the yeast needs oxygen. It may get this by turning the starchy flour in the bread dough into sugars or the baker may add a little sugar to the mixture. The sugar molecules are then broken up into carbon dioxide gas and ethyl alcohol. The gas forms the little bubbles in the dough which makes the bread rise.
This process takes time. The baker sets' his dough in a warm place while the little yeast cells grow, multiply and fill the dough with air bubbles. When the dough has puffed up to the right size, the baker pops it into a hot oven. The ethyl alcohol in the mixture evaporates, The heat is too much for the yeast cells, they stop growing and are destroyed The countless bubbles of gas are trapped inside the dough, which cooks firm. These pockets of gas make the finished loaf light anal spongy