igoo-i.] The Ripening of Cheese. 121 



with that of Duclaux, bacteria which are not lactic acid producers can 

 ripen cheese. 



3. The acidity at the commencement of ripening was not necessary 

 to bring about the solubiHty of the casein. 



In their second paper (1900). they criticised de Freudenreich's work 

 and report fresh results. De Freudenreich had shown that lactic acid 

 bacteria could attack and render soluble portions of the casein of viilk, 

 but Chodat and Hofman-Bang point out that it has not been shown that 

 the lactic acid bacteria can attack coagulated casein; and these two 

 substances are so different that the results which have been obtained 

 with the casein of milk cannot be applied a priori to coagulated 

 casein. 



These authors then experimented to see if the lactic acid bacteria 

 were capable of dissolving coagulated casein. They isolated five 

 different germs from Emmenthaler cheese, all of which produced lactic 

 acid, and others volatile acids, as formic, acetic, and valerianic. These 

 germs were grown on coagulated sugar-free casein, which had been 

 previously sterilized at 120' C, for three successive days. At the end 

 of three months, the acidity of the lactic ferments and the percentage of 

 soluble nitrogen were determined, and it was found that the bacteria 

 were well developed and were not contaminated, and that the quantity of 

 soluble nitrogen had not increased. All the cultures had a feeble 

 butyric odour. From this experiment, the authors concluded that de 

 Freudenreich was wrong when he said "That the lactic acid bacteria 

 play the principal role in the ripening of Emmenthaler cheese." 

 Further, they thought the lactic acid bacteria in their cultures grew at 

 the expense of the casein dissolved in the water used for moistening the 

 curd in the culture flasks. 



The lactic acid bacteria were also sown in flasks containing casein 

 modified by casease obtained from a species of Tyrothrix. The casein 

 was not dissolved by the Tyrothrix, and after the lactic germs had 

 grown on this substance for two-and-a-half months, there was no 

 increase in the percentage of soluble nitrogen. 



Again, they seeded sterilized casein with living Tyrothrix, allowed it 

 to grow until the curd was softened, without becoming liquid, and then 

 sterilized germs and casein together at 120° C. Upon the casein thus 

 prepared they placed a lactic acid bacillus, but with negative results, no 

 increase of soluble nitrogen was demonstrated, which showed that the 

 lactic acid germ had not been able to attack the casein. 



