36 THE BOOK OF CHEESE 



addition of lime salts will cause immediate coagulation. 

 (See also Spiro, 1906.) Hence the process of rennet 

 coagulation is a two-phase process ; the first phase is the 

 transformation of casein by rennin, the second is the 

 visible coagulation caused by lime salts. 



Furthermore, if the purest casein and the purest rennin 

 were used, Hammarsten always found after coagulation 

 that the filtrate contained very small amounts of a pro- 

 tein. This protein he designated as the " whey protein." 



In accordance with these observations, Hammarsten 

 (1911) explains the rennin action " as a cleavage process, 

 in which the chief mass of the casein, sometimes more 

 than 90 per cent, is split off as paracasein, a body closely 

 related to casein, and in the presence of sufficient amounts 

 of lime salts the paracasein-lime precipitates out while 

 the proteose-like substance (whey-protein) remains in 

 solution." 



By continued action of rennin on paracasein, a further 

 transformation has been found in several cases (Petry, 

 1906; Van Herwerden, 1907; Van Dam, 1909), but 

 perhaps due to a contamination of the rennin with pep- 

 sin, or to the identity of these two enzymes. The action 

 which forms paracasein and whey-protein takes place 

 in a short time (Hammarsten, 1896; Schmidt-Nielson, 

 1906). The composition and solubilities of paracasein 

 have received considerable attention. (See Loevenhart, 

 1904; Kikkoji, 1909; Van Slyke and Bosworth, 1912.) 

 It is more readily digested by pepsin-hydrochloric acid 

 than is casein (Hosl, 1910). 



53. Duclaux theory. Duclaux (1884) and Loeven- 

 hart (1904) and others do not accept Hammarsten's 

 theory ; but to most workers it seems probable, at least, 

 that the action of the rennin is to cause a cleavage of 



