CHAPTER XX. 

 SOUR-MILK BEVERAGES AND FOODS. 



I. IN the manufacture of most alcoholic liquors, 

 malt sugar or cane sugar are fermented by yeasts, 

 alcohol, along with a certain amount of carbon dioxide 

 gas and other substances being produced. 



Lactose, or milk sugar, although a disaccharide, and 

 similar in chemical composition to the sugars just men- 

 tioned, is not so readily fermented. A few yeasts are, 

 however, known which are able to form alcohol and 

 carbon dioxide from it, either directly, after hydrolysis, 

 by their own " inverting " enzymes, or indirectly, after 

 it has been decomposed into glucose and galactose by 

 bacteria. Similar alcoholic fermentation can be accom- 

 plished by certain bacteria. 



Generally, it would appear that the development of 

 lactic acid organisms checks the fermenting activity of 

 yeasts ; but a few examples are known of the produc- 

 tion of alcohol in milk soon after, or simultaneously 

 with, the formation of lactic acid, the one process no 

 doubt modifying the other. - * 



In various parts of the world alcoholic beverages or 

 foods containing lactic acid and alcohol are made from 

 the milk of domestic animals by ferments, the chief 

 of these being Kefir, Koumiss, and Mazun. Joghurt, a 

 sour-milk product, containing little or no alcohol, must 



also be noticed here. 



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