Fermentations of Milk. 61 



contains sugar, consequently, conditions are favorable 

 for yeast development. Milk cans in which sour whey 

 is carried, unless carefully washed, may serve to contam- 

 inate the milk to such an extent as to produce trouble in 

 cheese factories. 



The use of alcoholic drinks seems to have been more or 

 less common with nearly every type of people. The 

 Egyptians made beer from the grain they raised. The 

 nomadic tribes, having no grain, discovered methods of- 

 making alcoholic drinks from the milk furnished by their 

 herds of cattle, goats, and horses. In Russia such a fer- 

 mented drink, called koumiss, is made from mare's milk. 

 In other countries similar drinks, but prepared princi- 

 pally from cow's milk, are called kefir, matzoon, and 

 leben. They all have an acid taste due to the acid formed 

 by the lactic bacteria, and they contain nearly half as 

 much alcohol as a light beer. Such fermented milks- 

 seem to be more easily digested than raw milk, due un- 

 doubtedly to the fact that the casein is precipitated in a 

 finely divided condition and to the acid present. 



Bitter milk. Bitterness in milk may be due to bao 

 teria or to certain feeds. Ragweed is often claimed to 

 be the cause of such milk. If the feed is at fault, the 

 milk will show the bitterness when it is drawn from the 

 cow, and instead of increasing in intensity, as is likely to 

 be the case if the cause is bacterial, the taste usually be- 

 comes less and less evident as the age of the milk in- 

 creases. 



Various kinds of bacteria may cause the milk to taste 

 bitter. Some of the acid organisms cause such a change, 

 but more frequently the digesting bacteria are the source 

 of the trouble, and since these are more apt to develop in 

 pasteurized milk than in raw, a bitter fermentation is 



