68 THE: SEPARATION OF MH,K 



CHAPTER V. 

 THE SEPARATION OF MILK. 



Purpose. The purpose of separating milk is to obtain 

 cream. Cream is that portion of milk which contains a relatively 

 large proportion of its butterfat. In order to comply with the 

 legal Federal standard, cream must contain not less than 18 

 per cent of butter fat. 



The chief objects of using cream for butter making, instead 

 of churning milk, are first to reduce the volume of the fluid to be 

 churned and therefore to increase the capacity of the churn and 

 to reduce the labor and expense of churning; second to facilitate 

 the speed of churning; the richer the fluid is in butter fat, the 

 more readily do the fat globules unite into granules and the 

 shorter the time required for churning; third to increase the ex- 

 haustiveness of churning; milk or thin cream do not churn out 

 exhaustively, because the large volume of intervening liquid pre- 

 vents many of the fat globules, especially the small ones, from 

 uniting, thereby causing a relatively large number of these 

 globules to remain unchurned, to pass into the buttermilk and 

 to result in excessive loss of fat and a correspondingly small 

 churn yield. The churning of milk and thin cream further aug- 

 ments the loss of fat because it yields large volumes of butter 

 milk, thereby increasing the pounds of fat lost. 



Aside from the advantages of churning cream instead of 

 milk, large volumes of cream are separated for purposes other 

 than buttermaking, such as for table use, ice cream making, the 

 manufacture of whipped cream, etc. 



Principle of Separation. The separation of cream from milk 

 is based on the principle that the butter fat is lighter than the 

 other constituents of milk. At 60 degrees F. the specific gravity 

 of average milk is about 1.032, that of butterfat about .93 and 

 that of skim milk about 1.037. The fat globules, containing the 

 butterfat, therefore, yield to the gravity force and rise to the 

 surface. 



The principal agent retarding or preventing their upward 

 passage is the viscosity of the milk, which is largely due to its 



