BACTERIA IN CHEESE 



for the changes of casein, which constitute the ripening of the 

 cheese. 



Bacteria. The cheeses also contain bacteria in great numbers, 

 and usually in some considerable variety. Bacteria are present, 

 of course, in the original milk, and when the milk is placed in 

 the vat for curdling, their number will be considerable, differing 

 very slightly in the different kinds of cheeses. When the cheese 

 is made of sour milk (Cheddar Cheeses), their number will be 

 very high, for the reasons already indicated, whereas, if cheese 

 is made of sweet milk (Swiss Cheese), the number will naturally 

 be much less. Bacteria, too, are added to the milk with the 

 rennet which always contains vast numbers, some of which are 

 useful, some detrimental and some indifferent. 1 It has even 

 been suggested that the useful bacteria (acid bacteria) be 

 artificially added to rennet to hold the others in check. The 

 bacteria which are in the cheese at the beginning grow rapidly. 

 For some days after the cheese is made they increase rapidly 

 in numbers, reaching a maximum usually in about five days, 

 when they may be as many as 650,000,000 per gram." After 

 this they decrease. The decrease in cold-cured cheeses is less 

 rapid than in those cured at a higher temperature. The bac- 

 teria found are chiefly lactic acid bacteria, two common types 

 being found, the others that may be present at the outset soon 

 disappearing. 3 During the ripening they lose their acid- 

 producing power to a considerable extent, this fact perhaps 

 favoring the development of taints. 



Chemical Changes. There are thus, at least, two different 

 factors that may contribute toward the chemical changes of 

 ripening cheeses the growth of bacteria and the action of the 

 chemical ferments. Which of these two factors is the prom- 

 inent one in cheese ripening is a much discussed question. 



iThoni. Land. Jahr. d. Schweiz, 1906. 



2 Harrison and Connell. Rev. Gen. d'Lait, III., 1903. 



Harrison. Rev. Gen. d'Lait, V., p. 409, 1906. 

 3 Wenzirl. Cent. f. Bact., II., vi., p. 785, 1900. 



