194 AGRICULTURAL BACTERIOLOGY 



yeasts, and hence these organisms are certain to dominate 

 the fermentation in the fruit juice. 



The variety of yeast has much to do with the quality of 

 the wine or cider that is secured. The sugar is not changed 

 wholly into the two products named, but other substances 

 are formed which influence the flavor of the product. 



In the making of fermented and distilled liquors, such as 

 beer and whisky, and in the manufacture of industrial alco- 

 hol, starch is used. This is changed into maltose by the 

 enzymes of the malt, which is prepared by allowing barley 

 to sprout. In this process the enzyme is formed in such 

 abundance that a small amount of malt can be used to con- 

 vert the starch of a much larger amount of grain into 

 maltose, which is easily fermented by yeasts. The liquid 

 to be fermented will not contain sufficient yeasts to insure 

 rapid fermentation. It is also a favorable medium for 

 many kinds of bacteria. In order to avoid trouble there- 

 from, it is necessary to heat the liquid to free it from bac- 

 teria, and then to seed it heavily with selected yeasts. The 

 variety of organism that ferments the sugar will have 

 much to do with the flavor of the finished product. This is 

 of especial importance in the manufacture of beer. In 

 the manufacture of distilled liquors and industrial alcohol, 

 it is essential to employ a yeast that will be capable of pro- 

 ducing large amounts of alcohol before it is inhibited 

 thereby. 



The growth of harmful types of bacteria in the material 

 to be subjected to alcoholic fermentation may be prevented 

 by inoculating it with certain lactic-acid-forming bacteria. 

 The acid formed by them will not influence the growth of 

 the yeast, and since but traces of volatile acid are formed, 

 the quality of the distillate from the fermented liquor will 

 not be unfavorably influenced by the acid formed in the 

 fermented material. 



