PRESERVATION OF MILK. 341 



The acidity is expressed in terms of lactic acid. The pro- 

 teids are partly casein, but also consist of 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 

 fermentation are evidently impregnated with micro-organisms 

 and are placed in the milk until fermentation commences. 

 After this they are dried and kept for future use. Their origin 

 appears to be unknown. Many organisms have been found in 

 kephir grains, including bacteria and yeasts. It has been 

 stated that the kephir contains an enzyme lactase which 

 has the power of hydrolising milk sugar, thereby producing 

 glucose and galactose, and that yeast then attacks the former 

 as in ordinary alcoholic fermentation. 



Kephir resembles koumiss in composition, but contains less 

 alcohol and albumoses and more casein. 



MILK PRESERVATION. Milk is peculiarly liable to 

 undergo change under the influence of micro-organisms, for 

 the growth of which it serves as an excellent medium. In the 

 udder, milk is normally free from micro-organisms, but, unless 

 special precautions are taken, within a very short time after 

 milking it absolutely teems with them. 



In many cases examined, milk within a few minutes of 

 milking has been found to contain thousands of organisms per 

 cubic centimetre. The organisms, or their spores, are derived 

 from the air, the hands of the milker, the hair or teats of the 

 cow, and particularly from the vessels in which the milk is 

 received. 



The rate at which the bacteria multiply is largely dependent 

 upon the temperature. It was found that after fifteen hours 

 at 15, milk contained 100,000 bacteria per cubic centimetre, 

 while the same milk kept fifteen hours at 25, contained 

 72,000,000 per cubic centimetre, and at 35, 165,000,000 per 

 cubic centimetre." 



The importance of quickly cooling milk is thus evident, 



* Miquel, Oentral-B. fiir Agricult.-Chem. 1890, 575. 



