CHAPTER III 



Creaming 



CREAM is that portion of the milk rich in butter 

 fat which rises to the surface on standing or can 

 be separated by centrifugal force. 



Principle. The fat separates or rises to the sur- 

 face because of the difference in specific gravity be- 

 tween it and the milk serum; the latter, being the 

 heavier, is drawn down by the force of gravity, thus 

 crowding the fat to the surface and carrying with it 

 .some of each of the other solids. 



Specific gravity. The specific gravity of any- 

 thing is the weight of a definite volume of it com- 

 pared with an equal volume of water at 60 F. A 

 vessel that will hold 1,000 pounds of water will 

 hold 930 pounds of butter fat. The specific gravity 

 of butter fat is, therefore, 0.93, while the vessel of 

 whole milk would weigh 1,029 pounds (sp. gr., 

 1.029), and full of skim milk would weigh 1,035 

 pounds (sp. gr., 1.035). 



Lactometer. The lactometer is a weighted glass 

 bulb with a long stem at the top, graduated to show 

 the specific gravity by the depth to which it sinks 

 in the milk. It sinks until it displaces a volume 

 of milk equal to its own weight. The lighter the 

 milk, the deeper it must sink to displace a volume 

 equal to its own weight. Since the fat is light, the 

 richer the milk, the lower the specific gravity. The 

 determination of the specific gravity does not neces- 



