CHAPTER III. 



RAISING THE CREAM. 



COMPOSITION OF MILK CONDITIONS AFFECTING ITS CREAMING. 



In loo Ibs. of milk is found an average of 87.5 Ibs. watery 

 in which is dissolved 3.75 Ibs. casein and albumen, 4.5 Ibs. of 

 milk sugar, and 0.75 Ibs. of ash. In this watery solution 

 "serum" 3.5 Ibs. of butterfat, more or less, exists in emulsion. 



The specific gravity of the butter globules is less than that of 

 the serum (skim milk), that is, if a certain measure of water at 

 60 deg. weighs 1,000 Ibs., the same measure of skim milk will 

 weigh about 1,034 Ibs., of new milk about 1,030 Ibs., of cream hold- 

 ing 25 per cent, of fat 1,002 Ibs., of pure butterfat (at 100 deg.) 

 about 867 ibs. 



These facts explain the process of creaming, which goes on if 

 milk is left at rest. The fat globules together with some serum 1 

 rise to the top and form a layer of cream while the skim milk re- 

 tains more or less of the fat. 



Various conditions affect this separation, notably the depth 

 of the layer of milk and the temperature. It is evident that the 

 thinner the layer of milk the sooner will the butter globules make 

 their way to the top. 



Cooling will, as the late Prof. Arnold pointed out, affect the 

 serum and make it shrink faster than the butterfat, and thus in- 

 crease the difference in the specific gravity and cause the cream to 

 rise sooner. But while milk is being heated the opposite result is 

 obtained and the cream will rise more slowly. 



If, on the other hand, the temperature is stationary, the 

 higher temperature is the more favorable as the butterfat expands- 

 more (though more slowly) than does the serum. 



These facts explain why the "practical" dairymen often re- 

 port various results and demonstrate the necessity of varying the 

 system of setting according to the conditions ruling. 



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