CHEESE 617 



The culture-medium used for determining the number of bac- 

 teria is of importance, and may materially influence the result. 

 Eldredge and Rogers found that lactobaciUi increase in number 

 during the ripening period of Emmenthaler cheese, and these 

 would be overlooked if ordinary media were used. Special media 

 are necessary to demonstrate the presence of lactobaciUi. It is 

 probable, therefore, that our notions concerning the number of 

 bacteria present in cheese at different periods of the ripening 

 process will have to be revised. Esten and Mason found lacto- 

 baciUi in Camembert, Roquefort, Neufchatel, and Gorgonzola 

 cheese, and Evans, Hastings, and Hart found Bacterium casei in 

 Cheddar cheese. Bacteria of the group of lactobaciUi have been 

 frequently overlooked in dairy products because of the difficulty 

 in cultivating them. Therefore it may be expected that they will 

 be found, perhaps in large numbers, in niany cheeses besides those 

 mentioned. 



Frequently the curd is heated to about 55° C. This heating 

 has an influence on the texture of the cheese. If not heated the 

 curd is Uable to be soft, and if heated to high temperatures it 

 becomes hard. Heating has the additional advantage of destroy- 

 ing many bacteria and eliminating abnormal fermentations. For 

 example, members of the Bacillus coh group suffer by heating to 

 55° C, so that gassy fermentation is not likely to occur. The 

 lactic streptococci which survive produce acid in the curd by de- 

 composing the milk-sugar. 



The chief decomposition products of milk-sugar in cheese are 

 lactic acid and some volatile acids. The amount of acid in hard 

 cheese is 1 to 1.5 per cent.; in soft cheese, 2 to 4 per cent. These 

 figures represent the sum of free acid, acid phosphates, and 

 casein, which is a weak acid. If lactic streptococci are not pres- 

 ent in sufficient numbers to produce a relatively large amount of 

 acid, gas is liable to be formed by the members of the Bacillus 

 coli group. Gassy cheese is undesirable because large holes are 

 formed and a disagreeable, bitter taste is developed. The cheese 

 swells, and is known as being "swelled" or "buffed." In the mid- 

 dle portion of hard cheese conditions are anaerobic, so that strep- 

 tococci and lactobaciUi find favorable conditions for their growth, 

 while in soft cheese a small amount of oxygen remains in the 

 central portion. After all milk-sugar has been converted into 

 acid, conditions are ripe for the growth of molds, yeasts, and 

 liquefying cocci, which gradually neutralize the acid until in some 

 cheeses the reaction becomes alkaline. 



Digestion of casein commences in green cheese, if not earlier 

 in the milk. The acidity prevents peptonizing bacteria of the 

 Bacillus subtilis group from acting, but liquefying, acid-producing 



