76 Report of the Department of Bacteriology of thk 



of their product. However it was not until 1900^" that experi- 

 mental proof was broug^ht forth to show that this quickening of 

 the ripening process was due to the digestive action of a peptic 

 enzyme in the rennet. 



The part taken by the rennet enzyme in the ripening of cheese 

 has been discussed at length in Bulletin No. 233 of this Station 

 and the reader is referred to that bulletin for a detailed treat- 

 ment of the subject. In the present connection it will be 

 sufficient to point out that under normal conditions the change 

 of sugar into acid is necessary in order that the peptic enzyme 

 of the rennet may play its important part in the breaking down 

 of the cheese casein. As illustrative of this point there is 

 given below a summary of the chemical changes observed in 

 :wo of a series of cheeses made for the purpose of studying 

 :his relation. 



In order to measure the digestive action of the rennet it was 

 necessary to remove the other factors which might assist in the 

 breaking down of the casein. It has been shown in Bulletin No. 

 233 that a momentary heating to 85° C.will destroy the enzymes 

 in the milk itself and the milk used in making these cheeses was 

 heated above 95° C. for this purpose. In order to prevent bac- 

 terial action 2 to 3 per ct. of chloroform by volume was added 

 to the milk shortly after the above heating. 



The milk was made into cheese in the usual manner except 

 that calcium chloride was added to the milk to assist the curdling 

 action of the rennet. In cheese 6. 1 7 IV a total of . 2 per ct. lactic 

 acid was added in small diluted portions at intervals during the 

 process of manufacture to simulate the formation of the same by 

 bacteria under normal conditions. In 6. 17V this acid was 

 omitted. 



lOBabcock, Russell & Vivian. Ann. Rept. Wis. Station, 17:i02. (1900.) 

 Also Cetit. f. Bakt., II Abt., 6:817. (1900.) 

 Jensen. Landiv. Jahrb. d. Schweiz., 14:197. (1900). Also Cent, f, Bakt. 

 II Abt. 6:734. (1900.) 



