246 Journal of Agricultural Research voi. xm, no. 4 



OTHER STRAINS 



Not all the cheese streptococci can be classified in one or another of 

 the three groups which are described above, although most of the strains 

 which were studied agreed in every detail with those types. The irregular 

 strains will not be described in this paper for lack of sufficient data. 

 The study of a larger number of strains of streptococci from a wider 

 variety of fermented foods will most probably show that there are other 

 distinct types of flavor-producing streptococci, to which some of these 

 irregular strains may belong. Others are probably atypical strains. 



A few strains isolated from Roquefort cheese were non-lactose-fer- 

 menting and agreed in every way with the descriptions of 5. equinus, 

 but they have not been encountered frequently enough to suggest that 

 they may be of importance in cheese ripening. 



STREPTOCOCCUS X AND S. KEFIR AS RIPENING AGENTS OF CHEDDAR 



CHEESE 



As a result of an earlier work on Chedder cheese (8), the conclusion 

 was drawn that this type of cheese could not ripen normally without the 

 activity of several strains of streptococci. When the milk was pasteurized 

 for cheese making, the streptococcic flora consisted entirely of 5. lacticus 

 used as a starter. Such a cheese never developed the delicate flavor 

 typical of the Cheddar type, but instead it retained the acid flavor of the 

 curd until the influence of Bacterium btUgaricum became evident in the 

 late stages of ripening. The texture of the pasteurized-milk cheese was 

 also unlike that of raw-milk cheese. The pasteurized-milk cheese 

 remained white, opaque, and somewhat soggy, whereas the raw-milk 

 cheese became almost translucent, and developed a yellowish color. 

 The addition of one other strain of cheese streptococcus, together with 

 5. lacticus in the starter, modified the pasteurized-milk cheese favorably ; 

 but the typical Cheddar flavor was never obtained in the earlier series of 

 experiments. It was shown that several varieties of streptococci could 

 be isolated from a ripening Cheddar cheese made from raw milk, and it 

 appeared that the several varieties were necessary to produce typical 

 flavors. 



Two species of cheese streptococci have now been differentiated from 

 5. lacticus. A second series of experimental pasteurized cheese has been 

 made to show the effect of Streptococcus X and S. kefir on the ripening 

 process, with definite results. The studies of only three of the cheeses 

 need be mentioned to illustrate these results. The milk was pasteurized 

 for all three cheeses. One cheese was inoculated with a starter of 

 5. lacticus. It developed the acid flavor, and retained the white, opaque, 

 somewhat soggy curd characteristic of a cheese made in this manner. 

 The second cheese was made in just the same way, but had added to it 

 a starter of Streptococcus X in addition to the 5. lacticus starter. This 

 cheese was decidedly milder in flavor, the mildness being apparent as a 



