138 DAIRY BACTERIOLOGY 



being introduced with the "natural rennet"*. As the stomachs, 

 especially those of bad quality, also contain many harmful bacteria, 

 it is advantageous to inoculate the rennet at once with a mixed 

 culture of Thermobacterium helveticum and the mycoderma men- 

 tioned on p. 50 2 , or to secure favourable conditions for the lactic 

 acid bacteria simply by adding lactic acid (e.g., some boiled acid 

 Schotte) to the rennet. It is safer to use the pure factory made 

 rennet, together with pure cultures of Thermobacterium helveticum, 

 in sterile milk 3 . In order to secure the development of this 

 organism to the exclusion of other bacteria, the cheese must be 

 made warm and kept warm in the presses. This is achieved by 

 scalding at a comparatively high temperature, taking the curd 

 out of the warm whey in a lump, and above all by making the 

 cheeses so large that they will retain their heat for a long time. 

 Cheeses made in this way maintain a temperature of 50 to 35 C. 

 during the first twenty-four hours, and under these conditions 

 Thermobacterium helveticum is certain to obtain predominance. 



At the same time a lactic acid streptococcus (Sc. thermophilus) 

 having a high optimum temperature grows luxuriantly 4 . As this 

 organism does not attack casein, it hardly plays any important 

 part in the ripening of the cheese beyond the souring process, and 

 possibly assisting in the production of favourable conditions for 

 the growth of the lactic acid rod bacteria, in much the same way 

 as occurs in Yoghurt and similar products. 



While the drastic scalding weakens the gas-producing bacteria, 

 the high temperature of the cheese while in the press favours the 

 growth of the pseudo lactic acid bacteria, and if the milk was 

 dirty there will already be a very vigorous development of blow 

 holes. (Such a cheese (Presslis) develops a large number of pin- 

 holes.) Coli and aerogenes bacteria, as well as butyric acid 

 bacteria, may also develop at a later stage, and it is therefore 

 advisable to keep the cheese as cold as possible after it has left 

 the press, and until all the lactose has been fermented. Any 

 evolution of gas will do far more harm in the compact mass of 

 Emmental cheese than in most other cheeses from which the gas 

 can partially escape through the narrow fissures which mark off 

 the original particles of curd. For this very reason the normal 

 cavities or " eyes " are able to attain to a much larger size in 



1 Freudenreich and Orla Jensen, " Centralblatt f. Bakt.," Abt. 2, 1897, 

 Bd. III., p. 545. 



2 J. TJidni, " Bacteriologische Studien iiber Labmagen und Lab." 

 ("Landwirt. Jahrbuch der Schweiz," 1906, p. 181.) 



3 Rosengreen and Haglund, " Meddelande No. 101 fran Centraianstalten 

 for forsoksvasandet pa jordbmksomradandet," Stockholm, 1914. 



4 Orla Jensen, " Uber die in Emmenthalerkase stattfindende Milch- 

 siiuregarung." " Landwirt. Jahrbuch der Schweiz," 1906, p. 437. 



