314 SOUR-MILK BEVERAGES AND FOODS 



2. Kefir. The name Kefir is given to an acid alco- 

 holic beverage prepared from the milk of cattle, sheep, 

 or goats by inhabitants of the Caucasus. 



In the manufacture of it, milk is poured into skin 

 bags or " bottles," and fermented by means of Kefir- 

 grains. After two or three days, during which time it 

 is shaken occasionally, it is ready for consumption, and 

 forms a refreshing, foaming drink which, according to 

 some authorities, possesses considerable medicinal and 

 nutritive properties. 



The chief chemical changes occurring in the milk are 

 concerned with the milk-sugar. This constituent yields 

 lactic acid, alcohol, and carbon dioxide. Casein is pre- 

 cipitated by the acid, and on shaking the liquid breaks 

 up into 'fine flocculent particles which are readily 

 digested. 



The Kefir-grains, or active fermenting agents, in a 

 dry state, are small yellowish tough bodies, about the 

 size of large millet seeds or small peas. After soaking 

 in milk or water, they swell up and grow into gelatinous, 

 elastic convoluted structures which may become as large 

 as a waJnut. 



They are found to consist of a zoogloea of yeast-cells 

 and several kinds of bacteria which apparently carry on 

 a symbiotic existence. 



Many kinds of organisms are usually present, mostly 

 as unavoidable impurities ; according to Freudenreich, 

 only three or four are essential for the characteristic 

 fermentation of Kefir, namely, a non-sporing yeast or 

 Torula (Torula kefir] met with chiefly in the rind of the 

 grains, Bacillus caucasicus, and two forms of Streptococcus. 



The yeast has roundish-oval cells measuring 3 to 

 5 ,<* by 2 to 3 <tt, and produces a dark rose-coloured 



