RIPENING PROCESSES OF CHEESES 137 



correct understanding of the ripening processes which take place 

 in these cheeses. 



According to the author's researches, the proteolytic enzyme of 

 the lactic acid rod bacteria must be regarded as an endoenzyme, as 

 it is not liberated by the living cell, and its action recalls that of 

 erepsin, for it produces amino acids from the casein without 

 forming albumoses and peptones as intermediate products l . 

 The large amounts of amino acids which are found in many hard 

 cheeses are principally due to the action of this endoerepsin 2 . 

 The bacteria themselves take no part in the process, for most of 

 them will be dead before the bulk of the amino acids have been 

 produced 3 ; they do not thrive without sugar, and as all the 

 lactose in hard cheeses will have been fermented in the course of 

 a day or two, the ripening bacteria will already have reached their 

 maximum (over 100,000,000 per gram) by then, after which they 

 gradually fall off. Dead cells which are not exposed to desiccation 

 generally digest themselves more or less completely owing to the 

 action of the intracellular enzymes which thus set themselves free, 

 so that they become able to exert their digestive action on the 

 surrounding medium ; this is what happens in cheese where the 

 endoenzymes act under favourable conditions, not involving too 

 great dilution. The author has demonstrated the presence of 

 such enzymes in both hard and soft cheeses 4 . The fact that the 

 ripening of hard cheeses depends on enzyme action pure and 

 simple, and is not directly dependent on the action of living 

 bacteria, is also demonstrated by the ripening of these cheeses at 

 temperatures far below the minimum for cheese bacteria 5 . 



Of the various rod-shaped lactic acid bacteria isolated by 

 Freudenreich from Emmental cheese, one particular species, 

 Thermobacterium helveticum, seems to be indispensable for the 

 production of the typical sweetish taste, and it is extremely 

 interesting to see how the methods of manufacture, arrived at by 

 practical experience, favour the development of this bacterium 

 throughout the process. As the organism occurs in the fourth 

 stomach of the calf, it will develop freely when the stomach is 

 extracted in a warm place with " Schotte " (see p. 50). This is 

 the usual practice in the Swiss dairies, the ripening bacteria thus 



1 " Centralblatt f. Bakt.," 2 Abt., 1900. Bd. VI., p. 840, and 1904, Bd. 

 XIII., p. 521. 



2 Freudenreich and Orla Jensen, "Landwirt. Jahrbuch der Schweiz," 

 1899, p. 167. 



3 Orla Jensen, " Landwirt. Jahrbuch der Schweiz," 1906, p. 303. 



4 " Studien iiber die Enzymen im Ease," " Centralblatt f. Bakt.," 

 2 Abt., 1900, Bd. VI., p. 734. 



5 Babcock and Russel, Eighteenth Annual Report of the Wisconsin 

 Agricultural Experiment Station, 1901, p. 136. 



