20 Testing Milk and Its Products. 



which cream, butter, cheese, and condensed milk are 

 obtained. 



When milk is left standing for some time or subjected 

 to centrifugal force, it will separate into two distinct 

 parts, cream and skim milk. The proportion of each part 

 which is obtained and their chemical composition will de- 

 pend on the method by which the separation is effected; in 

 the so-called gravity process where the cream is separated 

 on standing either in shallow pans in the air, or in deep 

 cans, submerged in cold water a less complete separa- 

 tion is reached, less skim milk being obtained and this 

 being richer in fat than when the separation takes place 

 through the action of centrifugal force. 



In modern creameries the milk is now generally skim- 

 med by means of cream separators. Separator cream will 

 contain from 15 to 50 per cent, of fat, according to the 

 adjustment of the separator and of the milk supply; ordi- 

 narily it contains about 25 per ct. of fat. Cream of aver- 

 age quality, in addition to the fat content given, consists 

 of about 66 per ct. of water, 3.8 per ct. casein and albu- 

 men, 4.3 per ct. milk sugar, and .5 per ct. ash. 



The skim milk is made up of the milk serum (15) and a 

 small amount of fat, viz., toward .4 per ct. when obtained 

 by the gravity process, and less than .2 per ct. in the 

 case of separator skim milk. Milk set in shallow pans 

 in the air, or in deep cans in water above 60 F., will 

 give skim milk containing one-half to over one per ct. of 

 fat. Skim milk is used as a food for young farm animals 

 or as human food, and in this country in exceptional 

 cases, for the manufacture of cheese. 



25. Cream is used for the manufacture of butter or for 

 direct consumption. In the former case a certain amount 



