THE SEPARATION OF Miuc 69 



albuminoids, the casein, albumin, fibrin, globulin and other 

 similar constituents of a colloid nature inherent in milk and 

 cream, and to the milk sugar. If the viscosity of milk were no 

 greater than that of water, the fat globules would rise to the 

 surface instantaneously in a similar manner as oil poured 

 into water rises to the surface. 



In the separation of cream considerable portions of the 

 water and of the non-fatty solids of the milk are carried into 

 the cream. Generally speaking, the relation of solids not fat 

 to water in the cream is approximately the same as it is in milk. 

 The per cent of solids not fat in cream, however, is lower than 

 the per cent of solids not fat in milk, it varies inversely with the 

 per cent of fat. The higher the per cent of fat, the lower the 

 per cent of solids not fat. For further details on the composi- 

 tion of cream see "Composition of Cream," Chapter XVIII. 



Methods of Separation. The separation of milk, as practiced 

 on the farm and in the factory, is accomplished either by gravity 

 or by centrifugal force. In the application of these two funda- 

 mental systems of separation the following methods are used : 



shallow pan method 



Gravity separation 



deep-setting method 



~ , farm cream separator 



Centrifugal separation ' 



water-dilution (or hydraulic) method 



| power cream separator 

 Separation by Gravity. The milk is set at rest in a cool 

 place until most of the fat has risen to the surface forming a 

 layer of cream. The fat globules rise to the surface because of 

 the fact that they are lighter than the other liquid and solid con- 

 stituents 'of the milk. 



The Shallow Pan Method. The milk, preferably fresh from 

 the cow, is poured into a shallow pan usually, though not neces- 

 sarily, 15 to 25 inches in diameter and about 4 inches deep. The 

 pan is placed into a cool place, such as the cellar or it -may be 

 set in water. After 36 hours practically all of the fat capable of 

 rising to the surface by this method will have come to the sur- 

 face and the layer of cream thus formed is then skimmed off with 

 a spoon, ladle or specially constructed skimmer. The skim milk 

 usually contains about .5 to .6 per cent fat. 



