(e) Mix 1/8 cake yeast with a little lukewarm water. Stand in a warm place and after 15 minutes examine. Will yeast grow in water alone?
(f) Mix 1/8 cake yeast, 1 tablespoonful of sugar, and a little lukewarm water. Set aside in a warm place so that the yeast plants may grow. Then examine under the microscope. Are there any budding yeast cells? Make a drawing of the plants as they appear under the microscope.
Draw at least two practical conclusions from these experiments as to the use and care of yeast for bread making
[Illustration: From Farmers' Bulletin 398 FIGURE 86—GROWING YEAST
PLANTS]
PROPERTIES OF YEAST.—Yeast consists of a mass of microscopic plants (see Figure 86). When placed under proper conditions these plants grow rapidly, and in so doing they separate the sugar that exists in flour into carbon dioxide and alcohol. The carbon dioxide lightens dough. The alcohol passes off as vapor in baking.
Plants need moisture, warmth, light, and the food that is furnished by the air and soil for their growth. Yeast plants require all of these except light. They are not green plants, hence they need no light. Moisture is obtained from the water, milk, or other liquids used in bread dough. Yeast thrives at a temperature of 90 degrees F. It is killed by a temperature above 130 degrees F. Hence the yeast is mixed with lukewarm water. The other liquids that are added to it are of the same temperature. Also, the dough is placed in a warm place while it is rising, or while the yeast plants are growing. The food required for the rapid growth of the yeast is obtained from the protein and carbohydrates in the flour.
Compressed yeast cakes which are wrapped in tinfoil and received fresh at the market every day or two are the most satisfactory to use. This yeast must be fresh for successful bread making. It is fresh when it is of a light color, is free from dark streaks, and is crumbly in texture.
Stiff Dough.—Approximately four parts of flour to one of moisture are used for stiff doughs. When sufficient flour has been added to stiff dough, it should not cling to the sides of the mixing bowl. This is an indication to the pupil of the proper stiffness of the dough. The test applies, however, only when there is no coating of flour over the dough. One should remember that the softest dough will not "stick," if covered generously with flour.
General Suggestions for Bread Making.—Use wheat bread flour, or a combination of wheat bread flour with whole wheat, or graham flour, or with flour or meal made from other grains, in making bread. Flour should be kept in a dry place. It is well to warm flour for bread before using.
If milk is used, scald or boil it to prevent it from souring. Water should be boiled and then cooled (see Why Foods Spoil).