COMPOSITION OF MILK 105 



formed by the rising of tiny globules of butter-fat, 

 which were distributed evenly through the fresh milk. 

 The fat is so much lighter than the liquid in which it 

 floats that it will rise in the cream layer in about 

 twelve hours. This fat is a constituent of butter and 

 of some forms of cheese. 



3. Separation of casein. Add a few drops of acid, 



?3> 



cxr\-/ 



o 



o ^p 



o 



o" - 



<o;o 



V'aQS o 



O O OQ 



o ^'i? r^ 



o OQ vJ 



o O 



X^i 



o 



_ o 



Courtesy of B. F. Johnson Pub. Co. 

 a. Pure. b. Bacteria. 



FIG. 35. PURE AND IMPURE MILK 



vinegar will do, to the skimmed milk. Soon it will 

 thicken. Gently warm it now to about one hundred 

 degrees and carefully break the thickened surface with 

 a knife, and the skimmed milk will be seen to separate 

 into curd and whey. Now strain through a cloth, and 

 the casein will remain in the cloth, while the whey 

 passes through. This casein is one of the principal 

 parts of cheese. 



4. Separation of albumen. Slowly heat the whey 

 to 160 degrees Fahrenheit. It will become cloudy and 

 soon a soft jelly-like substance will collect on the sur- 



