CHAPTER V 



CREAM SEPARATION 



The practice of skimming cream from the top of a 

 vessel of milk is centuries old. Until recent years butter 

 was made from cream obtained in this way, or it was 

 made from whole milk. The modern introduction of 

 mechanical devices has unified and improved the process. 



SEPARATION BY THE FORCE OF GRAVITY 



39. Principle of separation. — The separation of cream 

 and skimmed-milk is possible because of the difference 

 in the specific gravity. The specific gravity of cream is 

 difficult to ascertain because of the exceedingly variable 

 fat-content and because there is a tendency for air to be 

 incorporated in it. For the purpose of separation, it is 

 sufficient to say that the specific gra\ity of milk-fat is 

 .91 or .92, and of milk-serum about 1.036. As long as 

 well separated skimmed-milk contains only .01 to .04 per 

 cent fat by the Babcock method of testing, it is con- 

 sidered to be all serum. In view of the fact that about 

 one-fourth to one-half of cream is milk-fat, it is readily 

 seen that cream is much lighter than skimmed-milk. The 

 force of gravity acts in direct proportion to the weight 

 of matter. Skimmed-milk is attracted to the earth with 

 greater force than milk-fat. The lighter substance, cream, 

 is crowded away from the earth, or is less attracted to it. 

 Thus the cream rises to the surface of the vessel that 



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