192 



THE PLANT WORLD 





O , 

 i§ ctioxicCe 



Bread making. Most of us are familiar with the process of 

 bread making. The materials used are flour, milk or water, or 

 both, salt, a little sugar to hasten the process of fermentation, or 

 " rising," as it is called, some butter or lard, and yeast. 



After the materials are mixed thoroughly the bread is put aside 

 in a warm place (between 70°-75° Fahrenheit) to " rise." If we 



examine the dough 

 after a few hours, we 

 find many holes in it, 

 which give the mass 

 a spongy appear- 

 ance. The yeast 

 plants, owing to 

 favorable condi- 

 tions, have grown 

 rapidly and made 

 bubbles of carbon 

 dioxide. Alcohol is 

 present, too, but 

 this is evaporated 

 when the dough is 

 baked. The baking 

 cooks the starch of 

 the bread, drives off 



flour 

 crater ondi 

 yeast 



is bcckect 



Explain the process by which bread becomes light ? 



the carbon dioxide and alcohol, and kills the yeast plants, besides 

 forming a protective crust on the loaf. 



Sour bread. In the " rising " of bread, bacteria always do 

 part of the work of fermentation. Certain of these plants form 

 acids after fermentation takes place. The sour taste of the bread 

 is usually due to this cause, and may be prevented by baking the 

 bread before the acids form, by having fresh yeast, good fresh 

 flour, and clean vessels with which to work. 



Importance of yeasts. Since yeast cells do not contain chloro- 

 phyll they cannot make their own food but must get it already 

 made. Their food consists mostly of fruit juices and other sugar 

 solutions. If a fruit syrup is left exposed to the air wild yeast 

 plants will settle on it, and multiply rapidly, causing fermentation. 



