CHAPTER XXIX 



CREAM SEPARATION 



The centrifugal cream separator is to the dairyman what 

 the reaper is to the grain grower, a harvester in fact (Figs. 112 

 and 116). 



ililk fat has a specific gravity of about 0.90 and skim milk 

 about 1.036. Therefore, the fat weighs 87 per cent as much as 

 the skim milk or milk serum in which it is floating. The 

 globules of fat, too, are so small, being only about j'lojooo of an 

 inch in diameter, that they rise slowly and with difiiculty in milk. 



For cream to rise naturally and even reasonably well the 

 milk must be kept cool and left undisturbed for about twenty- 

 four hours. Even then there will be a loss of butter fat of 

 between 0.25 and 0.50 per cent in the skim milk. 



If a herd of ten cows yields an average of 5000 pounds of 

 milk yearly, and the skim milk tests O.-IO per cent fat, there will 

 be a loss and virtual waste of about 160 pounds of butter fat. 

 This at 30 cents a pound is worth $48, or nearly enough 

 to pay for a good cream separator. 



This machine, now so common on the farms of the northern 

 and eastern states, is finding its way ontO' the farms of the 

 southern states also, as fast as livestock farming takes the place 

 of cotton growing. 



The centrifugal cream separator leaves only from 0.01 to 0.03 

 per cent of fat in the skim milk, yet it is based on the same princi- 

 ple that operated in the case of gravity creaming, namely : The 

 difference in the weight per volume of the two substances, the 

 milk fat and the milk serum. This is known as specific gi-avity. 

 The high speed of the bowl throws the milk out against the wall 

 with a force of from 80 pounds in the smaller, slower-running 

 machines to as much as 100 pounds per square inch with even 

 the larger hand separators. The fat is thereby literally squeezed 



inward while trying to fly outward, because the serum beino; 

 332 • " 



