THE PRODUCTION OF ALCOHOL 



221 



i o 



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take place; for example, that the casein is changed to peptone and 

 acid albumen. 



Kephir is prepared in the Caucasus from cow's milk. The kephir 

 granules are semi -translucent masses of a gelatinous consistency 

 (Fig. 127). These masses consist 



of bacteria and a yeast in sym- /.-'<>:. 



biotic association. The gelatinous "S % : - 



material is yielded by the bacteria, * 'I * 



and in this the yeast cells are em- 

 bedded. In the preparation of the 

 beverage the milk is raised to a 

 temperature of 18-19 C., the 

 kephir being then added. Fer- 

 mentation is allowed to proceed, 

 under constant agitation of the 

 liquid, for about 24 hours, after 

 which the liquid is bottled and 

 the fermentation completed in the 

 bottles. It results in a reduction 

 of the percentage of the milk- 

 sugar, the fatty matters, and the 

 proteids, whilst it creates about 1 

 per cent, of alcohol and a slightly 



larger amount of lactic acid. There are obviously two fermentations 

 taking place side by side, the yeast changing the milk-sugar into 

 alcohol, and the bacteria changing the milk-sugar into lactic acid. The 

 reduction of the fatty matters and the proteids may be due to still 

 other fermentations, or may be also used up in the two fermentations 

 just mentioned. 



Fio. 127. Kepbir (natural size) and the 

 species of bacteria of which it is composed. 

 (After Freudenreich.) 



3. THE PREPARATION OF VINEGAR. 



We have already mentioned the salient facts connected with acetic- 

 acid fermentation. In the manufacture of vinegar, which is practically 

 acetic acid, two methods are in general use. 



(a) In the first method, wine is the raw material. A number of 

 oaken casks are arranged in rows. In each is placed a small quantity 

 (half litre) of vinegar and four times that quantity of wine. The 

 vinegar is derived from a previous fermentation, and is added because 

 it contains acetic-acid bacteria. The room in which the casks are 



