198 BACTERIA IN MILK AND MILK PRODUCTS 



main one of milk-clotting rather than milk-curdling. The two chief 

 examples are the rennet fermentation of milk and the production of 

 casease. 



(4) The Alcoholic Fermentations of Milk — Lactose is not readily- 

 acted upon by yeasts though they have the power of breaking it up 

 and producing alcohol and carbonic acid gas. When it does occur the 

 percentage of alcohol is very small. The iirst change is the inversion 

 of the milk-sugar into dextrose and galactose, and the second is 

 fermentation of these sugars. 



Occasionally, alcohol is present in the milk of a dairy, as a sort of 

 by-product accompanying lactic fermentation, and alcoholic fermenta- 

 tion may, under exceptional circumstances, cause serious trouble to 

 the dairyman. But the chief illustrations of this fermentation in 

 milk are the well-known examples of the artificial beverages known 

 as koumiss (or kumiss, kumys) and kejphir (or kef yr, kefr), the former 

 a fermentation of mare's milk, the latter of cow's milk. Matzoon 

 and Lehen are two other examples of similar changes. 



Koumiss is made on the Steppes of South-Western Siberia and 

 European Eussia, by nomadic Tartars. It is not a simple process 

 nor a single fermentation. There is first a lactic fermentation 

 producing lactic acid, and secondly, a vinous fermentation result- 

 ing in alcohol. The former is produced by bacteria, the latter by 

 yeasts. In neither case is the process set up by a pure culture. 

 "The net change which has taken place in the original milk may 

 be summed up by saying that the sugar has been to a large extent 

 replaced by lactic acid, alcohol, and carbonic acid gas ; the casein has 

 been partly precipitated in a state of very fine division, and partly 

 predigested and dissolved, while the fat and salts have been left 

 much as they were." * The total proteid in koumiss is hardly less 

 than in mare's and cow's milk ; the fat is practically the same as in 

 mare's milk, and the sugar is reduced from about 5 per cent, to 1'5 

 per cent. The amount of alcohol in koumiss is as little as 1'7 per 

 cent., and there is not as much as 1 per cent, of lactic acid. 



Kephir, the second example named, is an effervescent alcoholic 

 sour milk prepared by inhabitants of the Caucasus from the milk of 

 goats, sheep, and cows. The process of fermentation is a double 

 one, and precisely parallel to that occurring in the production of 

 koumiss. Its method of manufacture is simply to add to milk a few 

 " kephir grains," allow the milk to stand for twenty-four hours at a 

 temperature of 17° to 19° C, pour off the milk and mix with fresh 

 volumes, and so on. Fermentation is complete in two or three days' 

 time, and the resultant fluid contains about 2 per cent, of alcohol, 

 being slightly more than in koumiss. 



* Pood and the Principles of Dietetics, by R. Hutchison, M.D,, F.R.C.P., 1902, 

 p. 136. 



