Apr. 22, i9i8 Streptococci Concerned in Cheese Ripening 249 



lactose, whether it results from the decomposition of the lactic acid, or 

 whether it comes from protein cleavage. 



The vigorous production of carbon dioxid by cultures of S. kefir explains 

 the hitherto unaccounted-for production of large quantities of that gas in 

 Cheddar cheese. Van Slyke and Hart {22) found that a normal Cheddar 

 cheese during 32 weeks' ripening produced carbon dioxid equal to 0.5 

 per cent of the fresh cheese. They found that carbon-dioxid production 

 in the cheese continued for months after the disappearance of the lactose, 

 and they state that apparently it came from reactions taking place in 

 some of the amido compounds. The source of the carbon dioxid has not 

 yet been determined, but from our results also it seems improbable that 

 it came from a decomposition of the lactose, since a vigorous decom- 

 position of the latter indicated by the increase in hydrogen-ion concen- 

 tration takes place in peptone-broth cultures, with the production of a 

 slight quantity of gas, whereas in digested milk an abundant gas produc- 

 tion accompanies the lactose fermentation. 



The results of cultural studies indicate that in peptone-yeast broth 

 free of fermentable substances, the protein cleavage takes place to 

 exactly the same extent in cultures of 5. lacticus and Streptococcus X. 

 Nevertheless the two organisms do not bring about the same changes in 

 the casein of ripening Cheddar cheese. It has been mentioned above 

 that the pasteurized-milk cheese ripened by 5. lacticus alone has an acid 

 flavor, whereas a cheese made in the same manner but with the use of a 

 starter of cheese streptococci in addition to the 5. lacticus starter develops 

 a milder flavor. To judge by the palate, the difference in flavor is pro- 

 nounced, but the difference in terms of hydrogen-ion concentration is 

 slight though definite. Two pasteurized-milk Cheddar cheeses inocu- 

 lated with 5. lacticus alone after about 10 weeks' ripening had a hydrogen- 

 ion concentration of Ph=5.7. A cheese made at the same time and 

 inoculated with 5. lacticus and Streptococcus X had a hydrogen-ion 

 concentration of Ph=5.9, and a fourth cheese inoculated with 5. lacticus, 

 Streptococcus X, and 5. kefir also had a hydrogen-ion concentration of 

 Ph=5.9. This slight difference of 0.2 Ph may have been responsible 

 for the difference in protein cleavage, which was evident in the cheeses 

 in the white, opaque, somewhat soggy mass in the case of those inoculated 

 with 5. lacticus alone, as compared with a more translucent, yellowish 

 mass in other cheeses. 



CHEESE STREPTOCOCCI IN SOFT-CREAM CHEESE 



The case is very much the same with soft-cream cheese as with Cheddar. 

 Cream cheese made from the best quality of raw milk develops a mild, 

 delicate flavor typical of this kind of cheese. Cream cheese made from 

 pasteurized milk and inoculated with a starter of S". lacticus develops an 

 agreeable acid flavor, particularly liked by many people, but on the 

 whole is inferior to the delicate flavors developed in cream cheese made 



