Composition of Milk and Its Products. 21 



cent, of fat and ordinarily contains about 83 per cent. ; 

 besides this amount of fat, butter is generally composed 

 of water, about 13 per cent., curd and milk sugar 1 per 

 cent., and salt 3 per cent. 



Butter milk has a composition similar to skim milk, 

 but varies much more than this product, according to 

 the acidity, temperature, and thickness of the cream, 

 and other churning factors. It contains about 9 per 

 cent, of solids, viz., milk sugar (and lactic acid) 4 per 

 cent., casein and albumen 4 per cent., fat .3 per cent., 

 and ash .7 per cent. 



26. The quantities of butter and by-products obtained 

 in the manufacture of butter are as follows : 1000 Ibs. 

 of milk of average quality will give about 850 Ibs. of 

 skim milk and 145 Ibs. of cream (separator slime and 

 mechanical loss, 5 Ibs.) ; this amount of cream will make 

 about 42 Ibs. of butter and 100 Ibs. of butter milk (me- 

 chanical loss, 3 Ibs.). 



27. In the manufacture of American cheddar cheese, 

 whole milk is heated to about 86 F., and a small amount 

 of rennet extract is added, which coagulates the casein ; 

 the albumen of the milk is not precipitated by rennet 

 and remains in solution (18). " Green " cheese, as taken 

 from the press, is made up, roughly speaking, of 37 per 

 cent, of water, 34 per cent, of fat, 24 per cent, of albu- 

 minoids (nearly all casein), and about 5 per cent, of 

 milk sugar, lactic acid, and ash (largely salt). In the 

 curing of cheese there is some less by drying, but the 

 main changes occur in the breaking up of the firm curd 

 into soluble and digestible nitrogenous compounds, pep- 

 tones, amids, etc. 



