24 DAIRYING 



261. The skimming efficiency of any method of cream sep- 

 aration is sometimes expressed in percentage which the cream fat 

 is of the whole milk fat. If 100 pounds of milk containing 4 per 

 cent. fat is so skimmed that 85 pounds of skim milk testing .2 

 per cent, fat is obtained from it, the .17 pounds of fat (or 85 X 2%) 

 subtracted from the fat in the whole milk, 4.0 pounds, leaves 3.83 

 pounds of fat in the cream. The per cent, which the fat recovered 

 in the cream is of the fat in the whole milk represents the skim- 

 ming efficiency of the method, or expressed in form of a propor- 

 tion, 4 :3.83 :: 100 :X = 9575%. 



This figure will be influenced both by the richness of the milk 

 and the amount of skim milk as well as by the test of the skim 

 milk. If the milk tested 3.0 per cent, fat, and .17 pounds fat was 

 left in the skim milk as before, the skimming efficiency i-s 

 3 minus .17=2.83, and then 3 : 2.83 : : 100 : X or 94-35 per cent. 



If 80 instead of 85 pounds of skim milk is taken and this tests 

 .2 per cent, fat, the skimming efficiency of milk testing 4.0 per 

 cent fat is 80 X .2 per cent, or .16 pounds, and 4 - - .16 3.84 

 pounds, which is the fat recovered in the cream and using the 

 same proportion, 3 : 3.84 : : 100 : X = 95.78 per cent., which repre- 

 sents the skimming efficiency. 



e. Centrifugal Cream Separation. 



262. It has been shown that there is a considerable loss of 

 fat when cream is obtained from milk by either of the common 

 gravity methods of cream separation described in the preceding 

 pages. These losses are now almost entirely overcome by the 

 modern "centrifugal" cream separator. This machine has made a 

 wonderfully rapid development in its construction since the time 

 it was first proposed for this purpose. It is now only about 

 twenty years old, though the principle of using centrifugal force 

 for separating the fat from the milk serum was recognized some 

 fifty years ago. 



263. Before considering the stages of development through 

 which the separator has passed it may be well to get a slight idea 



