CHAPTER XXXI. 



THE FERMENTATION OF CHEESE, AND ALLIED 

 DECOMPOSITIONS. 



175. The Composition of Ripe Cheese. 



THE conversion of the fresh curd into finished cheese is termed 

 ripening. We will, in the first place, consider this process from 

 the purely chemical side. It was explained in 144 that fresh 

 curd can be obtained from milk in two different ways, either by 

 precipitating with acids or by setting with rennet. In both cases 

 nitrogenous compounds are present in the coagulum, only in the 

 acid curd (" Quark ") they consist of casein, and in the rennet curd 

 ("Bruch") of paracasein. The cheeses obtained from the acid 

 coagulum are, with the sole exception of the " Glarner Schabziger," 

 of inferior quality, and only suitable for early consumption. These 

 have hitherto received but little attention from fermentation phy- 

 siologists ; consequently the following particulars are restricted to 

 cheeses obtained from rennet coagulum, which to emphasise the 

 point once more contain only one nitrogenous compound, namely, 

 paracasein. 



In contrast to this uniformity stands the variety of the nitro- 

 genous compounds present in ripe cheese. The first observa- 

 tion on this point was made in 1818 by J. L. PBOUST (I.), who 

 isolated leucine from ripe cheese. Some sixty years later (1880) 

 K. SIEBER (II.) detected the presence of tyre-sine in Koquefort 

 cheese. Nevertheless, these discoveries, as also those of two French 

 workers who will be mentioned later, were of a casual nature, the 

 first thorough attempt to follow the ripening process in a quantita- 

 tively analytical manner being made in 1882 by A. WEIDMANN (I.), 

 whose results, especially as regards the qualitative composition of 

 the cheese, were admirably supplemented by a later (1888) research 

 undertaken by B. ROSE and E. SCHULZE (L). These investiga- 

 tions were made in Switzerland on Emmentnal cheese, in which 

 the above-named chemists discovered a considerable amount of 

 leucine. On the other hand, comparatively little tyrosine was 

 found, and other amido-com pounds, as well as bodies of the 

 xanthine group, were altogether lacking. The presence of ammonia, 

 however, was readily proved, different samples being found to 

 contain from 0.16-0.44 P er cent, calculated to the dry weight. 

 The amount of nitrogen found in the form of ammonia, amido- 



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