THE YEAST PLANT 



:;:>:> 



Figure 374. — Yeast. 



cess alcohol is formed and carbon dioxide is sel five; 



(3) the yeast lives on the proteid substances in the flour; 



(4) both the gas which makes bread Light and the alcohol 

 are driven off by the 

 heat of the oven when 

 the bread is baked. 



Use is made of the 

 enzymes and yeast in 

 the making of beer, ah , 

 and porter. The pro- 

 cess of the manufacture 

 of these products is as follows: The grain, usually barley, 

 is soaked in water to soften it. The grain is kept warm 

 and moist until it sprouts, and in this condition is called 

 malt. It is then heated and crushed. Fermentation tal. 

 place when warmth and moisture are supplied, the enzyme 



diastase breaking up 

 the starch into sugars. 

 The liquid or wort from 

 this process is boiled 

 with hops. The wort 



is again fermented, this 

 time by tin- aid of yeast, 

 the action of which is 

 to break up the sugars 

 into carbon dioxide and 

 alcohol. Yeast of only 

 one kind is used (a pure 

 culture) and care is 

 taken to keep the tem- 

 perature favorable to its most rapid growth. As the yeasl 

 grows and breaks up t lie sugar, it forms quantities of gas 

 and alcohol. In bread these are temporary by-products 

 which are lost in the baking, but in the manufacture of 



Figure 375. — Fermentation Tubes. 



