166 Dairy Bacteriology. 



the production of these "off" flavors in the curd. If 

 these organisms are seeded in pasteurized milk and the 

 infected milk made into cheese, they develop odors that 

 are sometimes noted in factories troubled with taints. 

 These indefinite " off 7 ' flavors and odors are often in- 

 sufficiently pronounced to be given a name, consequently, 

 it will be impossible to describe them under any well de- 

 fined head. 



175. " Gassy" fermentations in cheese. One of 



the worst and at the same time most common troubles in 

 cheese-making is where the cheese undergoes a fermenta- 

 tion marked by the evolution of gas. The presence of 

 gas is recognized by the appearance either of spherical 

 or lens-shaped holes of various sizes in the green cheese; 

 often they appear in the curd even before it is put to 

 press. Usually in this condition, the curds look as if 

 they had been finely punctured with a pin, and are known 

 as "pin-hole" curds. Sometimes the gas holes are 

 larger, even approaching the large round so-called ' ' Swiss 

 holes." When the gas is abundant, the holes are more 

 apt to be restricted in size. The formation of gas may 

 continue to such an extent that the curd even floats on 

 the surface of the whey before it is removed. These 

 "floating curds" are permeated through and through 

 with gas bubbles, giving the curd a "spongy' ' appearance. 

 If "gassy" curds are put to press in this condition, 

 an abnormal change usually occurs within a few days. 

 The fermentation goes on in the green cheese causing it 

 to swell or ' ' huff, ' ' until it may be considerably distorted. 

 The gas diffuses with some difficulty in the new cheese 

 so that the mass rapidly swells. The fermentation may 

 be so energetic as to actually cause the cheese to crack, 

 owing to the pressure of the contained gas. In the se- 

 vere types of this gaseous fermentation, the product is 



