262 MODERN DAIRY PRACTICE. 



next the cheese made by means of rennet, we may first 

 mention that rennet forms an animal ferment prepared in 

 special glands in the third stomach of calves. In the co- 

 agulation of the casein by means of rennet, bacteria as 

 it seems, play only an insignificant part.* Rennet acts 

 best at 95-104 F. (35-45 C.). In adding the rennet 

 the milk is heated to a higher or lower temperature ac- 

 cording to the time in which the coagulation of the milk is 

 to take place. 



Among the kinds of cheese belonging to this group we 

 may distinguish between two subdivisions: 



1. The firm cheeses, requiring a long ripening period, 

 in the curing of which bacteria play the main part. 



2. The soft cheeses, requiring a short period of ripening, 

 the curing of which is effected not only by bacteria, but by 

 mold fungi. 



The manufacture of the firm cheese is very complicated 

 as now practised in cheese-factories; as we shall see, the 

 methods followed have been developed from experience. 

 Let us take a glance at the various processes in order to 

 ascertain what part the bacteria play in these. 



Methods of Manufacture of Firm Cheese. Milk used in 

 the manufacture of full cream cheese is usually recently 

 drawn and fresh. Its bacterial content is as a rule rather 

 low, but it is of course by far not germ-free. Macroscopic 

 as well as microscopic impurities will always be found in 



* The small number of bacteria added in the rennet in proportion 

 to those already present in the milk was first called attention to by 

 Bauinann (Inaug. Dissert. Univ. Konigsberg, 1893). He found that 

 under ordinary conditions the rennet added would supply only one 

 bacterium for every two thousand already present in the milk. See 

 also Pammel, Bull. 21, Iowa Experiment Station, p. 799. W. 



