go 



BACTERIA, YEASTS, AND MOLDS 



elderberries, blackberries, currants, raspberries, etc. Cider also 

 is an apple wine. The principles in the manufacture of these 

 homemade wines are the same as in the production of the 

 commercial wines. It must be remembered that in the United 

 States their sale or transportation is distinctly illegal. 



Whatever be the source of the yeast, the process of 

 wine making is simply an ordinary fermenting of the 



sugar. The carbon dioxide 

 that is produced is allowed 

 to pass off into the air undis- 

 turbed during the fermenta- 

 tion, and the liquid gradually 

 becomes filled with alcohol. 

 The final result is the 

 wine, which always contains 

 alcohol in small percentage. 

 After the yeasts stop grow- 

 ing, bacteria may develop in 

 the product and cause fur- 

 ther changes, so as to injure 

 its taste, or even totally change its nature, as in the forma- 

 tion of vinegar. (See Chapter XI.) 



Fig. 37. Organisms found upon the 

 skin of a grape and concerned in 

 the fermentation of wine. 



The Use of Yeasts as a Source of Carbon 

 Dioxide 



The chief use of yeasts in the household is not to pro- 

 duce fermented drinks but to raise bread. The raising 

 of bread by means of yeast has been brought to a state of 

 great perfection, so that the method of producing a desir- 

 able fermentation in bread dough by means of this product 



