256 ESSENTIALS OF BACTERIOLOGY 



be found all forms of air bacteria as well as molds and yeasts, 

 some beneficial, some harmful. The acid of grape- juice de- 

 stroys many of the harmful forms, but some persist and 

 must be dealt with by the wine-maker. 



The various yeasts produce alcohol from the sugar of the 

 grape. Vinegar bacteria likewise form a small amount of 

 acetic acid. The wine-maker's success lies in obtaining a 

 clean, unbruised grape, aiding the work of the wine yeasts, and 

 preventing the injurious forms from working. The grapes are 

 crushed and the juice allowed to settle. Pure cultures of 

 tested yeast are used as starters of fermentation. 



Fermentation is regulated by burning sulphur, which in- 

 hibits the growth of molds and harmful bacteria. After 

 fermentation is completed the wine is cleared and freed from 

 all organisms and kept as nearly as possible in a sterile con- 

 dition. 



Beer. The fermentation is produced by yeasts and with 

 a mixture of grains. Barley or other grains which have been 

 allowed to germinate produce malt. The malt contains the 

 enzymes which change starch into sugar. Then, by boiling, 

 the enzyme is destroyed and fermentation by yeasts is per- 

 mitted. The yeasts in modern breweries are pure cultures. 



Wild yeasts or lactic-acid bacteria may contaminate beer. 



Alcohol, brandy, and whisky are likewise the product of 

 yeast fermentation, some sugary substance furnishing the 

 material. 



