70 BACTERIA, YEASTS, AND MOLDS 



vigorous fermentation is started. The fermented mass 

 may subsequently be used directly for a beverage fer- 

 mented drinks, like beer, ale, etc. or the water may be 

 partly separated from the alcohol by distillation, produ- 

 cing a liquor with a much higher percentage of alcohol, 

 the distilled liquors, like rum, brandy, whisky, etc. 



In the making of wines the process is, in a way, simpler, 

 and reliance is usually placed upon the wild yeasts which 

 produce a spontaneous fermentation. The skin of the 

 grape becomes the lodging place of numerous micro- 

 organisms which collect there while the grape is growing. 

 These include molds and bacteria as well as yeasts, and 

 when the juice is squeezed from the grape it is certain to 

 contain some of this wild yeast. Fig. 37 shows some of 

 the wild yeast thus spontaneously inoculated into grape 

 juice. The juice is set aside and a spontaneous fermen- 

 tation begins. The fermentation is not very vigorous and 

 may require many weeks for its completion. In recent 

 years some vintners have adopted the plan of adding to 

 the grape juice cultures of chosen varieties of yeast for 

 the purpose of hastening the fermentation and making it 

 more reliable. The success of the plan is still somewhat 

 doubtful, and this method of wine making has not been 

 very widely adopted up to the present time. 



So sure is the grape juice to contain yeasts that unless 

 some means of preventing their growth is adopted fer- 

 mentation cannot be avoided. In making what is called 

 unfermented grape juice the yeasts are destroyed by heat. 

 The grape juice is heated to a temperature of about 

 170 for a few minutes. This operation is usually per- 

 formed twice, after which the wine is bottled and sealed. 



