XV. 



MILK AND MILK PBODUCTS 



343 



The sweetened product keeps better, especially after the hermetically 

 sealed tins, in which the product is sent out, have been opened. 



The directions on these tins generally recommend the contents to 

 be mixed with from five to seven volumes of water. The resulting 

 mixture is obviously much poorer in fat and proteids than genuine milk. 



The degree of concentration and the fat content vary greatly in the 

 different commercial brands. 



Milk Powder is made by evaporating milk in thin layers under re- 

 duced pressure, and scraping off the resulting film. The fat in the resi- 

 due renders the production of a powder difficult, because of its viscosity, 

 and in much of the yellowish-white commercial product, the amount of 

 fat present is less in proportion to the other constituents than would 

 be present in the residue obtained from whole milk. The powder 

 shaken up with water yields a fairly good substitute for fresh milk. 



' Koumiss is an alcoholic beverage produced from milk by fermenta- 

 tion. As already stated, lactose does not readily undergo alcoholic fer- 

 mentation. The sugar of mares' milk, however, readily ferments, and an 

 alcoholic liquid can be prepared by the addition of a little koumiss, or 

 even sour milk, to mares' milk. Such beverages have been long known 

 in Tartary. 



By the addition of a small quantity of cane sugar and yeast to 

 cows' milk, a similar beverage can be prepared. 



The casein at first coagulates, but afterwards partly redissolves, and 

 does not appear to be so liable to coagulation under the influence of 

 gastric juice as is that of fresh milk. Koumiss is thus very easily 

 digested and acts both as a stimulant and as a food ; it is therefore used 

 for invalids. Ginzberg l finds that the lactic and alcoholic fermen- 

 tation proceed concurrently, and that the casein is partially hydrolysed 

 and robbed of its mineral constituents. 



The following analyses of koumiss are given by Wiley : 



The acidity is expressed in terms of lactic acid. The proteids are 

 partly casein, but also contain albumoses. The carbon dioxide gives 

 an effervescent character to the bottled koumiss. 



Kephir is a similar product made in the Caucasus from cows' 

 milk. The " kephir " grains which are used to start the fermenta- 

 tion are evidently impregnated with micro-organisms and are placed in 

 the milk until fermentation commences. After this they are dried and 



1 Biochem. Zeitsch., 1910, 1 ; Jour. Chem. Soc., 1911, Abstracts, ii. 140. 



