Ann Thompson, age 10, of Moroland, Georgia, for her question.
How do they make commercial yeast?
Yeast is a valuable protein food. It contains nearly as much protein as beef and far less fats. These facts make it a valuable body building food. If the world's meat supply ran short, we could manufacture yeast diets to take its place, With proper yeast culture, 5,000 pounds of yeast becomes 25,000 pounds in ten and one half hours. This 122 tons of yeast contains as much protein as there is in 80 pigs.
Yeast culture is the growing of yeast, much as a farmer cultivates crops. For yeasts are really tiny plants of the mushroom family, Like mushrooms, they need shade, warmth and rich food. When these conditions are ,just right the yeast will double its weight in two hours. The culture is done in a large vat where food is mixed with the yeast cells and the temperature is carefully controlled.
The yeast food, in liquid form, is first poured into the culture vat. It is called wort and. there are various recipes for preparing it. The main ingredient is sugar, which may be added in the form of molasses, Yeast cells cannot digest starch, which is the cheapest of foods, We cannot feed starch to yeasts, but we can feed them starch which has been converted into sugar: Starchy grains of corn are pulped and cooked. The mash is mixed with ground barley, malt and rye. Sprouted barley is added and this converts the starch mash into malt sugar.
Malt sugar provides the yeast with a balanced diet, If molasses is used, nitrogen in the form of ammonium salts must be added to the recipe. The first 20,000 gallons of wort poured into the vat is a very watery mixture, containing only a trace of yeast food. A milky wad of 300 pounds of yeast is added to the tank and air is piped into the mixture.
The little oval‑shaped yeast coils eat and grow. In about two hour, each is ready to multiply by dividing into two cells. The culture is now ready for a second feeding. About 800 gallons of stronger wort is added and smaller amounts of stronger and stronger food will be added until the entire mixture is converted into yeast.
The job takes 10 to 12 hours. Just as corn becomes pork when eaten by a pig so this malt sugar is eaten and turned into yeast. The finished product is a creamy colored soup. The liquid is filtered out and the yeast drained dry. It is pressed into cakes and kept under refrigeration until needed. The bulk of this yeast will be used for making our bread.
The little plant cells refuse to grow in the cold. But when mixed with warm water and g little sugar, they wake up and start to eat and multiply. is they eat they give off carbon dioxide gas which makes bubbles in the bread dough. The oven is too hot for the yeast cells so, after baking, they grow no more. They have made the bread light and added protein, which is quite a good days work.