YEASTS A SOURCE OF ALCOHOL 



71 



The process is really the same as that of preserving 

 food by canning, which will be described later, the only 

 essential difference being that the grape juice does not 

 require boiling for its preservation. It will be noticed 

 from Fig. 37 that there are other organisms besides 

 yeasts upon the grape skin. These may have some effect 

 upon the wine, but very little is known in regard to the 

 matter. 



In the household yeasts are occasionally used in the 

 same way, solely for the alcohol they develop. This use 

 is practically confined to the 

 manufacture of a few of the 

 homemade wines which are 

 produced from juices of fruit 

 such as grapes, elderberries, 

 blackberries, currants, rasp- 

 berries, etc. Cider 2\%Q) is an 

 apple wine. The principles 

 in the manufacture of these 

 homemade wines are the 

 same as in the production of 

 the commercial wines. The 



Fig. 37. Organisms found upon the 

 skin of a grape and concerned in 

 the fermentation of wine. 



fruit juice, which contains a considerable quantity of easily 

 fermentable sugar, is expressed from the fruits and mixed 

 with water. Commonly the fruit juice is not sweet enough, 

 particularly if a sweet wine is desired. In the manufac- 

 ture of most homemade wines, therefore, sugar is added. 

 The amount varies widely with the kind of fruit used, 

 being greater for sour fruits, and it varies also according 

 to whether a sweet or sour wine is wanted. The juice is 

 then left to ferment spontaneously under the influence of 



