Household science and arts

Yeast is a very tiny little plant. It has no stem or leaves, or flowers, or seeds. For it is a one-celled plant that grows by budding. That means that one cell grows from another. Digitized by Google Your teacher will draw blackboard pictures to illustrate the growth and appearance of yeast. When seen under a microscope, the yeast plant appears as a tiny oval cell which is nearly colorless. Yeast plants are found growing in the air, on the skins of fruits, and on the broken skins of decaying fruit. It is also cultivated for use in distillery work and in bread making. Market Forms of Yeast. — Compressed yeast, one of the market forms of this plant, is skimmed from the top of fermented liquor, washed several times, strained and pressed, mixed with a small amount of starch, and made into cakes. These are wrapped in tin foil to keep the yeast from drying. When fresh, it is firm, moist, and creamy in color, and one cake contains milUons of yeast plants. Dry Yeast is another market form. It is made by mixing fresh yeast with starch or meal until a stiff dough is formed. Liquid Yeast is a third market form. In olden days it was very common indeed. It is now called baker's yeast and is made from potatoes, sugar, and a small amount of hops and water, added to a little yeast to start yeast plants growing. The potato, hops, sugar, and water make a substance very favorable to the growth of the yeast plant. Experiments with Yeast. 1. Mix 1 yeast cake, 2 ts. sugar, and i c. lukewarm water. Place part of mixture in three different test tubes. 2. Place test tube No. 1 in water at 32° F. and keep it at that temperature for 1 hr. 3. Place test tube No. 2 in water at 212° F. and keep the water at that temperature for 1 hr. 4. Place test tube No. 3 in lukewarm water and keep it at between 75° and 90° for 1 hr. At end of an hour examine the three tubes, and compare the results. Inferences by the class. Digitized by Google Growth of Yeast Plants. — Yeast plants grow best at a temperature of 70 to 85°. The freezing point (32° F.) stops the growth of the plant but does not kill it. It may be killed by pouring hot water (130°) on it. From these facts you can learn that yeast will not grow and make bread rise when it is cold, nor can the yeast cause bread to rise after it reaches a temperature which kills the yeast plant. When dough sours J the yeast has been allowed to grow too long. When yeast is added to a batter, it is like scattering into it millions of little living cells which grow rapidly imder certain conditions or when given air, warmth, moisture, and a sweetened substance. When yeast grows, it changes the sweetened substance into alcohol and a gas called carbon dioxide. This change is called fermentation. Bread Making. — Bread must be mixed, kneaded, raised, molded or shaped, raised a second time, and baked in order to produce an appetizing and wholesome mixture of the substances in it. The process of bread making consists of mixing the dry materials', adding the yeast and lukewarm liquid, mixing or kneading it thoroughly to insure thorough mixing of the ingredients and letting the mixture rise in a warm place to double its bulk. This order may be reversed, starting with the liquids and adding dry materials to them. The water should be boiled before and the milk should be scalded. All the liquids should be cooled to lukewarm temperatures before adding the yeast. If the dough rises too long or over twice the bulk, the dough becomes sour. To prevent this cut or knead it down when it is twice its size, and let rise again before shaping it. After it is shaped, the dough is put into a greased pan; it is then allowed to rise again to double its size, and then is baked in a hot oven. Digitized by Google