284 THE BOOK OF CHEESE 



remains to contaminate the normal eye. The nitrogen 1 

 is included from the original air. Propionic acid is 

 formed at the same time as the eyes, and they are 

 said to be the result of a propionic ferment of lactic 

 acid. The interior of the cheese is anaerobic, due to 

 low permeability and high oxygen-absorbing quality. 

 This propionic bacterium cannot, however, account for 

 all the carbon dioxide produced. 



After the eyes have started, their further development 

 depends on temperature and humidity of the air, and on 

 the moisture of the cheese, as regulated by the amount 

 of salt used. The first room has a temperature of 70 F. 

 to start the eyes, which is later lowered in the second 

 curing-room to about 60 to check the development. 

 When any local fermentive action starts, it may be 

 checked by rubbing salt on the affected part. The 

 humidity of the room is very important, because a 

 cheese will quickly dry out in a dry room, due to evap- 

 oration from the surface. To prevent this, it is well 

 to spray the floor with water, or to have a steam jet in 

 the room. 



If the curd has been cooked too long the cheese may 

 be too dry. Such cheeses may be piled two or more deep 



1 Clark, W. M., On the formation of "eyes" in Emmenthal 

 cheese, Jour. Dairy Sci. 1 (1917), no. 2, pages 91-113. 



Among important studies of Swiss cheese ripening are the 

 following: Freudenreich, E. v., and Orla Jensen, Ueber die in 

 Emmentalerkase stattfindende Proprionsauregarung, Centralb. f . 

 Bakt. etc. 2 Abt. 17, page 529. 



Jensen, Orla, Biologische Studien iiber den Kasereifungs- 

 prozess unter spezieller Berucksichtigung der fltichtigen Fett- 

 sauren, Centralb. f. Bakt. etc. 2 Abt. 13 (1904), page 161. 



Eldredge, E. E., and L. A. Rogers, The bacteriology of cheese 

 of the Emmenthal type, Centralb. f. Bakt. 2 Abt. 40 (1914), no. 

 1/8, pages 5-21. 



