Thomas doyle, age 10, of albany, n. Y., for his question:

What is yeast made from?

For thousands of years our ancestors used yeast to make their bread light and Spongy. But they did not know why it worked. About 100 years ago, science discovered that yeast grows and multiplies. This information showed how supplies of yeast can be Produced as needed.   A tablet of pressed yeast or a package of crumbly yeast does not seem to be alive. But it is. It is a population of miniature members of the plant world. About 5000 Yeast plants measure an inch, and each is a single, living cell. Its larger cousins Are mushrooms; its smaller cousins are molds and mildews. A yeast cell is a fungus Plant. All life springs from life. A yeast cell comes from a yeast cell and tries to Hand on life to a new generation just like itself. We cannot make or creat the Supplies of yeast we need to make our bread light and spongy   or the different yeasts We need to make wines and vinegars. We must start with a colony of original yeast and Encourage the microscopic ce11s to grow and multiply. Most yeast cells are sausage shaped, some long and some almost round. The living Protoplasm of each ce11 is encased in a ce11 wall. We cannot say that a yeast cell Eats as we do. But it absorbs food through its ce11 wall and uses it to thrive and Multiply. Yeast for baking may be grown in a tall tank of lukewarm mash with plenty Of air blown into the bubbling mixture. The mash is a mixture of nitrogen foods. It may be ground from rye and corn, Mixed with malt and molasses. Phosphate chemicals are also added to the brew. Under The right conditions, each yeast ce22 may consume twice its own weight in food every  Hour. When ready, it sprouts a bud. The daughter bud is fully grown in an hour, arms Mother and daughter each sprout a new bud. At this rate, the thriving yeast doubles  Itself every hour.  more   

After about l2 hours, a supply of new yeast is ready. All the food supplies have Been consumed, and the tank is fi11ed with creamy colored soup. The liquid is dried And becomes a pale, crumbly material with a tangy, yeasty smell. Some of this yeast Will be pressed into tablets.   In dry yeast, the living cells are waiting for the right conditions. When mixed With a batch of bread dough, they start to grow and multiply. Then they absorb and Give off alcohol and gassy carbon dioxide. The gas fills the dough with spongy Bubbles. In the hot oven, the yeast ce11s are ki11ed and the alcohol escapes. The Gassy bubbles remain, making the bread light and spongy.