722 Reading-Course for Farmers' Wives. 



alcohol which the yeast makes out of sugar. The yeast plants grow 

 best at a medium temperature, about 75° to 90° F., which is an average 

 " sumnier heat." Above 90°F. they cannot grow so well, but the bacteria 

 grow better. 



The little yeast plant, although so small and simple in structure, is 

 endowed with many of the powers of the trees and vegetables or such 

 higher plants. It requires food, has a certain range of temperature in 

 which it grows best, will be injured or killed by too high or too low 

 temperature, or by too little moisture. If it be given the conditions which 

 are favorable, it will feed, grow rapidly, and reproduce itself by swelling 

 out one part into a bud which may or may not break away from the 

 mother cell. The most favorable temperature for the rapid growth of 

 the yeast plant, as already said, is 75 °F. to 90^ F. Below this it will 

 not grow rapidly and therefore cannot do much work. At much above 

 90° it will be killed, and a dead plant cannot work any more than a 

 dead animal. 



The work of the yeast plants is to change the sugar in the sponge into 

 two substances — alcohol, and a gas which is called carbon dioxid. The 

 millions of little bubbles cannot break through the sticky gluten of the 

 flour, so they raise the whole mass. When the bread is baked the gas 

 is dissipated, the gluten walls of these bubbles are hardened and the 

 little holes remain, filled only with air. The alcohol, too, is driven off 

 by the heat. 



It is very difiicult to keep weeds out of the vegetable garden because 

 their seeds are carried to the soil in so many wa}^s. When they have 

 sprouted or grown a little, they may be pulled up easily. In the bread- 

 garden we want only yeast to grow, but it is very difficult to have this, 

 when neither the good plants nor the weeds ever become visible. 



In no way does household bacteriology interest the housekeeper so 

 much as in the baking of her bread. Compressed yeast and dry yeast 

 cakes are a mass of yeast plants mixed with some form of starch and 

 pressed into cakes. One cake may contain one-half billion yeast plants. 

 They should contain only one species of yeast, but oftentimes other 

 plants gain access to the mixture. If a compressed yeast cake has been 

 kept over a day or two it begins to turn dark and to soften. This is a 

 sign that the yeast plants are dying and bacteria have gained access 

 to the cake, thus causing decay. The cake should then be discarded, 

 for it will not make good bread. If dough is left too long or if it is kept 

 too warm, the yeast plants become weakened and then the bacteria 

 which may be present grow and produce an acid, making the bread sour. 

 We scald the rtiilk used in making bread in order to destroy the bacteria 



