Milk Fermentations. 63 



Another alcoholic beverage that is in common use 

 among the people of Caucasus is kephir (also kefyr, kefir) . 

 This is a sour, effervescent alcoholic fluid prepared from 

 the milk of goats, cows, or sheep. The direct cause of 

 the fermentation is the so-called kefir grain, a yellowish 

 mass about as large as a walnut that is added to the milk. 

 These grains are left in the milk for about a day; the 

 milk is then poured off, and the grain dried and pre- 

 served for future use. This milk after being mixed with 

 fresh milk is kept in leather flasks and soon a mixed fer- 

 mentation sets in. 



This alcoholic change has been studied considerably 

 from a biological point of view 1 , but even yet is not 

 thoroughly understood . It is evidently a mixed fermenta- 

 tion, and one in which no single organism can produce 

 all the essential ingredients. The sugar of milk is par- 

 tially converted into alcohol, but at the same time the 

 casein is coagulated and digested to a certain extent, so 

 that the process is quite complicated. Some of the or- 

 ganisms isolated have been found to be able to produce 

 a change allied to that seen under natural conditions. A 

 yeast form is probably the main cause of the alcoholic 

 fermentation, while bacteria change the other constitu- 

 ents of the milk. 



62. Butyric acid fermentations. The fermentation 

 characterized by the production of butyric acid is also a 

 class fermentation that is caused by the action of a num- 

 ber of different aerobic and anaerobic bacterial species. 

 This decomposition process is common in boiled milk and 

 as a secondary fermentation in sour milk. 2 For a long 

 time it was thought that the butyric acid change in sour 

 milk was a continuation of the lactic fermentation, but 



1 Freudenreich, Landw. Jahr. d. Schweiz, 10: 1, 1896. 



2 Hofmann, Ann. de Sci. Nat., 11: 5, 1869. 



