400 EXPERIMENT STATION RECORD. 



made from pasteurized milk without tlie addition of chldroforui; (3) in cheese con- 

 taining eonnnercial pepsin and micro-organisms; and (4) in comparison with com- 

 mercial pepsin on casein in milk and paracasein dilactate. Detailed data for the 

 experiments are given in an api)endix. The results are summarized as follows: 



"In the case of every experiment made, there was little or no digesting action by 

 either rennet enzym or commercial pe])sin in the aljseni-e of ac-id, while the action 

 was marked in the i)resen(-e of acid. 



"In the absence of acid in cheese no paracasein lactate is found, and little or no 

 proteolysis occurs; in the presence of acid in the cheese i)aracasein monolactate is 

 formed and digestion takes place, the rennet ferment being the active agent. The 

 ability of rennet enzym to convert paracasein into soluble nitrogen compounds 

 appears to depend upon the presence of acid, resulting in the formation of paracasein 

 monolactate. 



"Rennet enzym and commercial pepsin act essentially alike in forming soluble 

 nitrogen compounds when comjjared with each other in the case of cheese, milk, and 

 paracasein dilactate. 



"In the case of both rennet enzym and commercial pepsin, the chemical work 

 performed by the ferments is confined mainly to the formation of the ])aranuclein, 

 caseoses, and peptones, while only small amounts of amids are formed, and no 

 ammonia. 



"Rennet enzym is really a peptic ferment. 



"Salt, in the proportions found in normal cheese, appears to have little effect upon 

 the action of rennet enzym in cheese ripening. The experiments on this point are, 

 however, not regarded as conclusive. 



"The abnormal conditions present in many of the experiments, such as pasteur- 

 ized milk, calcium chlorid, and chloroform, would tend, if they had any effect at all, 

 to decrease the digestive action of rennet enzym. Our results, therefore, may prop- 

 erly be regarded as representing the minimum effect of rennet enzym in cheese 

 ripening. 



"The digestive action of rennet enzym does not appear to extend to the formation 

 of compounds that produce tlie flavor of c-heese." 



Conditions affecting- chemical chang-es in cheese ripening, L. L. Van Slyke 

 and E. B. Hakt {Xew York State Sta. Bui. 236, pp. 1.33-163).— Thin bulletin giv-es the 

 results of a study of the chemical changes taking place in the nitrogen compounds of 

 cheese as affected l:)y time, temperature, moistvire, size of cheese, salt, rennet, and 

 acid. The casein of milk is converted into paracasein hj the action of rennet, after 

 which paracasein monolactate, paranuclein, caseoses, peptones, amido compounds, 

 and ammonia comj)ounds are formed in approximately the order mentioned. The 

 bulletin deals with the quantities of these different compounds, and their relations to 

 one another, in Cheddar cheese, made for the most part according to usual commer- 

 cial methods and ripened under controlled conditions. From 4 to 8 cheeses, weigh- 

 ing 10 or 30 lbs. each, were made from the same lot of milk in each experiment. 

 Detailed analytical data are given in an appendix, and the results are summarized 

 by the authors as follows: 



" The amount of soluble nitrogen compounds increases as cheese ages. The rate 

 of formation of these compounds is more rapid in the earlier stages of ripening, 

 about two-thirds being formed during the first 3 months and over 90 per cent in the 

 first 9 months of an 18-month period of study. 



"Soluble nitrogen compounds increase in cheese rijiening (juite closely in projjor- 

 tion to increase of temperature. Between the limits of 32° F. and 70° F. there was 

 an increase of 0.5 per cent of soluble nitrogen compounds for an increase of one 

 degree of temperature. The amido compounds and ammonia were more abundantly 

 formed, and they steadih' accumulated in cheese cured at higher temperatures. 



" Cheese containing more moisture, other conditions being uniform, generally con- 

 tains larger amounts of soluble nitrogen compounds, especially after the early stages 

 of ripening. 



