BUTTER-MAKING 225 



of samples did not vary widely from these average figures, some 

 rather wide variations were found. Thus, the extremes in 

 percentage were: fat, 73.49 and 87.39; moisture, 10.13 and 

 20,65 ; salt, 0.68 and 5.65 and curd, 0.12 and 3.42. Lee found 

 the average composition of 574 samples of butter collected from 

 several states during a period of one year to be : water 13.54 

 per cent, fat 83.20 per cent, salt 2.25 per cent, and casein and 

 ash 0.9 per cent. These figures represent the normal composi- 

 tion of butter. The composition will vary according to the 

 methods used in its manufacture and within certain limits 

 can be controlled by the butter-maker. The fat does not 

 usually vary more than 3 or 4 per cent. The salt may be varied 

 at will, but usually is between 1.5 and 3.5 per cent. The normal 

 variation for the curd or casein is from about 0.6 per cent to 

 1.5 per cent. The greatest variation occurs in the water, 

 which may vary from 12 per cent to nearly 16 per cent, that 

 being the legal limit for this constituent. Ordinary variations 

 in composition do not affect the quality of the butter nearly 

 as much as does the quality of the cream used or the methods 

 of manufacture. 



CKEAMING 



For butter-making the milk-fat is removed from the milk in 

 the form of cream which should contain from about 30 per cent 

 to about 45 or possibly 50 per cent of fat. This separation of 

 the fat in the form of cream is possible, because of the difference 

 in the specific gravity between the fat globules and the other 

 constituents of the milk. If milk is allowed to stand undis- 

 turbed, the fat globules will slowly rise to the surface and can 

 then be skimmed off in the form of cream, the rapidity and 

 completeness with which the fat globules rise to the surface 

 depending on the difference in specific gravity between the fat 

 globules and the other elements in the milk, and on the viscosity 

 of the milk-serum. Anything which affects either of these 



