ix] CHEESE 155 



in his power to decide which role they shall perform. 

 When, however, our knowledge of the bacteria impli- 

 cated in these processes has become sufficiently exact 

 to admit of our isolating them and preparing them 

 in pure cultures, we shall then be in a position both 

 to make butter and cheese from fresh milk which 

 has had little time to develop any undesirable kind 

 of fermentation, or from sterilised milk, by simply 

 adding the pure culture of the proper bacteria, and 

 thus secure uniformly good results. 1 



Composition of Cheese. Cheese, as we have al- 

 ready said, varies very much in composition. Some- 

 times it contains but a small proportion of fat, while 

 in other cheeses the fat is the most abundant con- 

 stituent. There is nearly always present a small 

 quantity of lactic acid. Good cheeses contain from 

 30 to 35 per cent of water ; inferior kinds from 38 

 to 45 per cent. Eich cheeses contain from 25 to 35 

 per cent of fat, sometimes even more. The casein is 

 very variable in amount. In skim -milk cheese it 

 amounts to as much as 50 per cent ; while in some 

 of the soft cheeses it may be as low as 11 to 12 per 

 cent. The following table illustrates the composition 

 of the commoner kinds of cheese 2 : 



1 That there is great room for improvement in the manufacture of 

 cheese maybe inferred from the statement that, according to Dr. Conn, 

 sometimes as high as 50 per cent of the cheeses made in a factory are 

 worthless, or comparatively worthless, owing to abnormal ripening. 



2 Johnston's Elements of Agricultural Chemistry, Seventeenth 

 Edition, by C. M. Aikman, p. 461. 



