THE CHEMICAL CONSTITUENTS OF MILK 313 



be kept scrupulously clean. The cow-houses should be fre- 

 quently whitewashed. Manure should not be moved, and 

 dry fodder (hay, straw, etc.) or litter should not be distributed 

 during or soon before milking. The dust of hay and straw 

 swarms with bacteria. The fore milk, i.e. the first pull or two 

 of each teat, should be rejected, or at least kept separate from 

 the bulk. It always contains more bacteria, and is much 

 poorer in fat. It can be used in other ways. Finally, the 

 milk should, if possible, be cooled immediately after it is 

 drawn. The bacteria do not multiply, or only very slowly, at 

 temperatures below 10 C. If these precautions are observed 

 the milk will rarely turn sour in less than 24 hours even in 

 warm weather. They are, of course, of greater importance 

 when the milk is sent long distances by rail. 



Fermented Milk. Milk may be preserved not only by 

 preventing fermentation, but also by promoting it. When the 

 changes are properly regulated the fermented products form 

 wholesome if not particularly agreeable foods. Joghurt is the 

 name given to a product of this kind, which is extensively 

 used in Eastern Europe. It is made by introducing a lactic 

 ferment, and warming the milk to a temperature of about 

 40 C. for 10 to 12 hours. It is described as a thick coagu- 

 lated substance with a not unpleasant (acid) taste and smell. 

 A very similar product called " lapper milk " is used in some 

 parts of Scotland. It is simply milk which has been allowed 

 to stand till enough lactic acid is formed to curdle it. In 

 both cases the fermentation is almost purely of the lactic type, 

 and very little if any alcohol is formed. 



When treated in a different manner milk undergoes 

 alcoholic fermentation. Koumiss, Kefir, and Mazun are all 

 products of this kind. Koumiss is perhaps the most widely 

 known. It was originally prepared in Tartary from mare's 

 milk. It is very highly charged with carbon dioxide formed 

 by the fermentation, and effervesces strongly. A very similar 

 product can be made from cow's milk by adding cane sugar 

 and fermenting with brewer's yeast. A palatable imitation 

 can also be prepared by adding a quart of butter milk and 

 2 ozs. of sugar to a gallon of fresh whole milk ; the mixture is 



