234 FERMENT A TION 



215. The Cause of Fermentation. Although alcoholic 

 fermentation, and the fermentation which goes on in raising 

 dough, were known and utilized for many years, the cause of 

 the phenomenon was a sealed book until the nineteenth 

 century. About that time it was discovered, through the 

 use of the microscope, that fermenting liquids contain an 

 army of minute plant organisms which not only live there, 

 but which actually grow and multiply within the liquid. 

 For growth and multiplication, food is necessary, and this the 

 tiny plants get in abundance from the fruit juices ; they feed 

 upon the sugary matter and as they feed, they ferment it, 

 changing it into carbon dioxide and alcohol. The carbon di- 

 oxide, in the form of small bubbles, passes off from the fer- 

 menting mass, while the alcohol remains in the liquid, giving 

 the stimulating effect desired by imbibers of alcoholic drinks. 

 The unknown strange organisms were called yeast, and they 

 were the starting point of the yeast cakes and .yeast brews 

 manufactured to-day on a large scale, not only for bread 

 making but for the commercial production of beer, ale, por- 

 ter, and other intoxicating drinks. 



The grains, rye, corn, rice, wheat, from which meal is 

 made, contain only a small quantity of sugar, but, on the 

 other hand, they contain a large quantity of starch which is 

 easily convertible into sugar. Upon this the tiny yeast 

 plants in the dough feed, and, as in the case of the wines, 

 ferment the sugar, producing carbon dioxide and alcohol. 

 The dough is thick and sticky and the gas bubbles expand 

 it into a spongy mass. The tiny yeast plants multiply and 

 continue to make alcohol and gas, and in consequence, the 

 dough becomes lighter and lighter. When it has risen suf- 

 ficiently, it is kneaded and placed in an oven; the heat of the 

 oven soon kills the yeast plants and drives the alcohol out of 

 the bread ; at the same time it expands the imprisoned gas 



