TYPES OF CURD 201 



The author's results showed that the type of fermentation 

 was determined by a combination of factors which varied in 

 different samples. The chief factors were the total and relative 

 numbers of the various groups of organisms which constituted 

 the bacterial flora. 



When the total bacteria were very low the fermentation was 

 usually of the A type, i.e., very little visible alteration occurred 

 in the physical appearance of the sample, and a smooth acid 

 flavour was produced. The acid producers were so few in num- 

 bers as to be unable to produce, under the incubator conditions, 

 sufficient acid to coagulate the caseinogen. This is the dis- 

 tinguishing feature of type A. In types B, C, and D, there was 

 a distinct coagulation, but the character varied in each group 

 according to the organisms associated with the acid producers. 

 The acid producers in each case produced their effect, and if the 

 ratio of acid formers to gas formers were large, little or no evi- 

 dence of gas formation was observed. As this ratio decreased 

 furrows became evident and numerous gas bubbles were found 

 enclosed in the curd, whilst in extreme cases the gas formation 

 was so marked as to force the cream layer to the top of the tube. 

 As any gas formed previous to the production of a firm curd 

 would be lost without leaving any evidence, it follows that any 

 gas observed must have been produced after coagulation and in 

 a medium of increased acidity. To effect this the proportion of 

 colon organisms must be considerable, as, otherwise, their 

 development would be retarded by the metabolic products of 

 the acid group. Very many samples, however, were observed 

 to produce gas bubbles in the fermentation test, and yet con- 

 tained originally less than one B. coli per cubic centimetre. 

 In these cases either the small numbers of the B. coli must have 

 increased very rapidly in proportion to the acid formers or be 

 of an acid resisting type. At ordinary temperatures (50 to 

 60 F.), the colon content usually continued to increase until 

 about 0.7 per cent of acidity, calculated as lactic acid, was 

 produced. .. 



The results also showed that the same type of fermentation 



