140 DAIRY BACTERIOLOGY 



acids, whereby the viscosity of the liquid is decreased, and as 

 increasing amounts of the curd become soluble the pores in the 

 cheese will become larger. The salt which at an earlier stage 

 tended to cause the cheese to swell now has the opposite effect, 

 but as the rind prevents contraction of the mass as a whole, the 

 pores must become still larger. The salting and drying of the 

 cheese finally bring about the precipitation of the sparingly 

 soluble amino acids as white crusts, and these so-called " salt 

 stones " may be distributed throughout the whole mass. 



The reason why the ripening of Emmental cheese has been 

 discussed so thoroughly is that this cheese has been studied more 

 thoroughly than any other. In this respect, the large-holed 

 Swedish manor farm cheese, which resembles the Danish-made 

 Swiss cheese, comes next. According to Gerda Troili-Petersoris 

 researches J , the ripening of this cheese depends on peptonising 

 tetracocci in addition to the lactic acid rod bacteria, and the 

 formation of eyes on certain glycerine-fermenting aerogenes 

 bacteria as well as the propionic acid bacteria. According to 

 Gorini 2 , peptonising tetracocci also play an important part in the 

 ripening of Parmesan cheese, in the making of which the curd is 

 scalded at a high temperature ; this cheese differs from Emmen- 

 tal in being prepared without the addition of strongly acidifying 

 lactic acid rod bacteria, a dough made from chopped calves' 

 stomachs being used instead of the acid " natural rennet " de- 

 scribed above. The peptonising cocci, just mentioned, generally 

 develop freely in the fresh curd, for, unlike the tyrothrix bacteria, 

 they can grow in the presence of acid. They are, however, 

 quickly suppressed if too much acid is present, and will therefore 

 be most prominent in cheeses which sour slowly or in cheeses made 

 from milk which has been ripened at a temperature below 15 C., 

 as they grow better than the true lactic acid bacteria under 

 this temperature. The proteolytic enzyme secreted by the 

 peptonising tetracocci is less sensitive to acid than the erepsin of 

 the lactic acid rod bacteria, and its mode of action is intermediate 

 between that of the latter and that of rennet. It would therefore 

 appear to be best defined as an " exotrypsin" The best investi- 

 gated of these cocci is Tetracoccus liquefaciens, which produces 

 the characteristic taste of Tilsit cheese or Russian Steppe cheese, 

 and there is no doubt that it plays an important part in the 



1 "Centralblatt f. Bakt.," 2 Abt., 1909, Bd. XXIV., p. 343. 



2 Among the numerous papers by this investigator, special mention may 

 be made of " Kecherches sur les coccus producteurs d'acide et de pressures 

 du fromage " (" Eevue generate du lait," 1910, vol. 8, p. 337). The true 

 significance of the action of the peptonising micrococci in the ripening of 

 cheese was first pointed out by Weigmann, 1896 (" Centralblatt f. Bakt.." 

 2 Abt., Bd. II., p. 151). 



