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 " Glarner Schabziger," of inferior quality, and only suitable for 

 early consumption. These have hitherto received but little attention from 

 fermentation physiologists ; 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 nitrogenous compounds 

 present in ripe cheese. The first observation on this point was made in 1818 by 

 J. L. PROUST (I.), who isolated leucine from ripe cheese. Some sixty years later 

 (1880) N. SIEBER (II.) detected the presence of tyrosine in Roquefort 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 quantitatively 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 under- 

 taken by B. ROSE and E. SCHULZE (I.). These investigations were made in 

 Switzerland on Emmenthal 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-compounds, 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-acids, 

 and other compounds distinct from albumen and peptone, in three kinds of this 

 cheese, ranged between 1.22 and 1.48 per cent. ; i.e. about one-fifth of the total 

 quantity of this element present. Among the albuminoid constituents special 

 mention must be made of caseo-glutin, a body allied to the peptones, and one that 

 must be considered as among the chief products of the ripening process, since it 

 constitutes 20 per cent., and even more, of the total dry matter. In addition, 

 there was found (along with a small quantity of peptones) another albuminoid 

 body, recognised as paracasein. To the list of the constituents of ripe Emmenthal 

 cheese still another unit phenylamidopropionic acid, was added in 1887 by the 

 labours of F. BENECKE and E. SCHULZE (I.) 



Several other kinds of cheese were included in the scope of these investigations. 

 In harmony with the similarity existing between the methods employed in their 

 preparation the qualitative composition of Spalen cheese was found to resemble 

 that of the Emmenthal product. Peptone was also detected in Gruyere, Vacherin, 



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