RIPENING PROCESSES OF CHEESES 131 



milk may be allowed to ripen at a temperature favouable to the 

 development of good lactic acid bacteria (15 to 20 C.), or an appro- 

 priate amount of buttermilk, starter or other lactic acid cultures 

 may be added. The longer' the time occupied in making the 

 cheese, the sourer will be the curd. The "temperature of the curd 

 when placed in the cheese press determines the species of lactic 

 acid bacteria which shall obtain predominance. If scalding is 

 omitted, and the curd is cooled by kneading after the whey has 

 been run off, the bacterial flora will be quite different from that 

 which results when heat is applied and the curd is taken direct 

 from the warm whey. By scalding and carefully cutting the curd, 

 the separation of the whey will be facilitated ; a means is thus 

 afforded of shortening the curd forming process, and of regulating 

 the degree of acidity of the cheese. 



As nearly half the natural acidity of milk is due to the 

 casein, it follows that the whey must have a much lower acidity 

 than the milk from which it was made. In order to control 

 the process of souring during cheese making, the whey may be 

 titrated at different stages. Although the indications thus 

 obtained will be of some value, they are far from accurate, 

 and should be supplemented by a careful examination of the 

 consistency of the curd. On coagulation, with careful treat- 

 ment of the milk, most of the bacteria become enclosed in 

 the curd and consequently lactic acid fermentation will take 

 place far more rapidly within the curd than in the whey 1 . In 

 the curd, however, most of the acid produced will be neutralised 

 by the lime of the casein and the phosphates ; accordingly it 

 will sometimes be found that in spite of a vigorous lactic acid 

 fermentation the acidity of the whey may remain unaltered 

 during the process, or even decrease as happens in the making 

 of Emmental cheese, for owing to the fact that the whey is 

 scalded at a fairly high temperature, the loss of carbonic acid 

 more than counterbalances the gain in lactic acid taken up by the 

 whey from the curd. If the bulk of the whey is removed at an 

 early stage, the remaining whey will be more acid than usual at 

 the end of the process as the lactic acid which has diffused out of 

 the curd will have been diluted to a less extent. When the casein 

 loses its lime it becomes, as van Slyke and Hart were the first to 

 show 2 , fairly readily soluble in a 5 per cent, solution of sodium 

 chloride, especially at 50 to 55 C., but this property is lost in the 

 presence of an excess of acid. The author has shown 3 that this 



1 Orla Jensen, ' w Tiber die im Emmenthalerkiise stattfindende Milch - 

 sauregarung." " Landwirt. Jahrbuch der Schweiz," 1906, p. 287. 



2 New York Agric. Exp. Station, Bull. No. 261, 1905. 



3 " Zeitschrift f. physiologische Chemie," 1914, Bd. XCIIL, p. 283. 



92 



