242 THE CHBMISTEY OF THE FARM 



decomposition, but the absolute weight of fatty acids 

 remains the same. Young cheese contains a small 

 quantity of lactic acid. 



Composition. — The different qualities of cheese are 

 chiefly determined by the richness of the milk ; its 

 sweetness or acidity ; the proportion of rennet used ; 

 the temperature of curdling ; the scalding and manipu- 

 lation of the curd ; the pressure to which it is subject ; 

 the temperature of the cheese-room, and the age of the 

 cheese. Curdling at a low or medium temperature, the 

 omission of scalding, and a light pressure in the cheese- 

 frame, are employed in the case of cheese intended to 

 ripen early and develop mould. 



The chemical composition of cheese exhibits great 

 variations, the differences, both in the original compo- 

 sition and in the alterations due to age, bemg very 

 considerable. Soft cheese contains most water, usually 

 40 — 50 per cent. Skim milk cheese may also reach 

 40 per cent, of water. Ordinary Cheddar will contain 

 27 — 34 per cent. The percentage of fat depends, of 

 course, on the materials employed. Cream cheese 

 may contain 50 — 60 per cent. ; Stilton, 35 per cent., 

 or more ; Cheddar and Cheshire, 24 — 33 per cent. ; 

 Gloucester (made from partly skimmed milk), 22 — 25 

 per cent. ; Skim milk cheese, 17 per cent. ; and 

 cheese from separated milk, 1 per cent. The percentage 

 of casein is determined by the percentages of water 

 and fat present ; in Cheddar and Cheshire it will be 

 24 — 36 per cent. ; in skim milk cheese it may exceed 

 40 per cent. Cheese generally yields about 4 per cent, 

 of ash ; skim milk cheese, 6 per cent. A great part of 

 the ash consists of common salt. 



