2o8 CHEESE 



198. Estimation of Fat. ' 



The material remaining in the basin after the 

 estimation of moisture (above), is transferred by means 

 of a spatula to a fat-free cartridge, and the latter 

 placed in a Soxhlet extractor. The basin is well 

 washed with ether, the washings being poured on to 

 the cartridge in the extractor. 



Extraction with ether is then carried out as usual 

 for two hours, the contents of the cartridge then placed 

 in a mortar, well ground, returned to the cartridge, 

 the mortar washed out as before, and the extraction 

 proceeded with. This procedure is necessary as a 

 certain proportion of the fat globules are embedded 

 in the mass of the cheese, and hence do not come into 

 contact with the ether. It may be necessary to repeat 

 this grinding three or four times, until it is found that 

 the contents of the weighed flask, after driving off the 

 ether, do not increase further in weight. 



A modification of Gerber's method for the estimation of fat 

 in milk (p. 185) may also be employed in the case of cheese. 



Approximate Percentages of Fat in Different Cheeses. 



Cream . . . . .40 



Gruyere . . . . .30 



Dutch . . . . .20 



Skim-milk ..... 10 



Nitrogenous Substances. 



The nitrogenous substances present in cheese may be divided 

 as follows : (i.) insoluble proteins ; (ii.) water-soluble proteins, 

 amides, etc. ; (iii.) ammonia and ammonium compounds. 



During the process of ripening of cheese the proportion of 

 these different nitrogenous constituents varies, the general tendency 

 being to split up complex insoluble proteins into simpler soluble 

 proteins or amino-bodies, and ammonia. These changes are 

 due to the action of micro-organisms and also of enzymes, which 



