Edwin Wheland, age 12, of Youngstown, Ohio, for his question:
What do they use to make yeast?
Yeast, as we know, is that wonderful springy stuff used to make our bread light and spongy. Believe it or not, it is alive. And the only way to get more of it is to coax it to multiply. This is done by providing it with warmth, moisture and helpings of sugary food. People have been doing this since the first bakers baked yeasty loaves in the coals of the family campfire.
We share our world with multitudes of mini plants and animals, most of them too small for our eyes to see. These midget populations include thousands of different yeasts, all of them single celled relatives of the fungus plant family. Like their larger mushroom relatives, the yeasts need warmth and moisture, shade and rather rich diets.
When all these conditions are just right, one pound of yeast can multiply and become 30 pounds of yeast in about 12 hours. There are numerous wild yeasts with known and unknown qualities. But most of the types we use are well known, highly purified tame yeasts. The most common domestic types are used in bread and bakery products.
The multiplication problem begins with a pure culture of this or that suitable yeast strain. This wad of original seed is made of living, sausage shaped cells, which measure about 25,000 in an inch. The project is performed in an enormous vat, fitted with pipes to let in air and more pipes to keep the mixture warm. Maybe the original seed yeast is a 500 pound wad of pale cells. Moisture and food are added intervals, and the multiplication proceeds at a fantastic rate.
A thriving yeast cell multiplies by budding an identical daughter cell. In a couple of hours the well fed daughter sprouts a budding daughter and so on. After 10 hours, the original 500 pounds of yeast becomes 2,500 pounds of identical yeast. This astounding multiplication continues at the same rate as long as the soupy mixture gets regular helpings of suitable food, warmth and moisture.
As a rule, the first meal is a watery mixture of sugary molasses with a small helping of ammonium salts to provide needed nitrogen. The feasting seed cells gorge, multiply and double in weight in about two hours. Then the batch is ready for a more concentrated meal. In two hours, the mother and daughter cells sprout new daughter cells and the yeast doubles again. After 10 or 12 hours, all the food is converted into yeast and the soupy mixture is ready to be processed for market.
When the moist mixture is dried, the lively cells sink into a dormant state. They may be packaged like dried crumbs or mixed with starch to form yeast cakes. When the dormant cells are mixed with warm water and sugar they wake up and start multiplying again. But this time they work to add spongy lightness to our bread