DAIRY PRODUCTS 



375 



489. Separating cream from milk ; the problem. Butter-fat 

 globules are lighter than the other constituents of the milk, and 



rise to the surface. The , , 



specific gravity 1 of the 

 fat globules is .9, while 

 that of skim milk is 

 i .034. Cream is merely 

 milk in which the fat glob- 

 ules have been greatly 

 concentrated. Ordinary 

 whole milk contains 

 about 5 per cent of 

 butter fat, while cream 

 may contain as much as 

 40 or 50 per cent. 



FIG. 187. Types of milk pails 



The pail at the left is the better, because the hood 

 helps to keep the dirt out of the milk 



490. Gravity systems. For a long time cream was separated 

 by gravity, a system which consisted of setting the milk in 



B C D 



FIG. 1 88. How the separator saves butter fat 



This illustration shows the relative loss of butter by different methods of skimming the 

 milk from one cow in a year. A, centrifugal separator, 1.2 pounds loss ; B, deep setting, 

 10.1 pounds loss ; C, shallow pans, 26.2 pounds loss ; >, water dilution, 49.5 pounds loss. 

 (Photograph from Purdue University) 



shallow pans, allowing the fat globules to float to the surface, and 

 then skimming them off. This was known as the shallow-pan 



1 The specific gravity refers to a comparison of the weight of a given quan- 

 tity of fat globules or skim milk to the weight of a like quantity of water, both 

 being at o degrees C. 



