THE GAS PRODUCTION OF STREPTOCOCCUS KEFIRS 



JAMES M. SHERMAN 



From the Research Laboratories of the Dairy Division, United States Department of 

 Agriculture, Washington, D. C. 



Received for publication August 7, 1920 



In her work on cheese streptococci, INIiss Evans (1918) has 

 noted the presence in Cheddar cheese of gas-forming strepto- 

 cocci apparently similar to a streptococcus first isolated by von 

 Freudenreich from kefir. It was observed also that the gas, 

 which consisted entirely of carbon dioxid, was produced much 

 more abundantly in some media than in others. For example, 

 in trypsin-digested milk a relatively large amount of gas was 

 formed while in lactose broth a much smaller volume was 

 obtained, notwithstanding the fact that the latter medium 

 underwent a vigorous acid fermentation. This indicated that 

 the source of the carbon dioxid might be something other than 

 the sugar. 



Aside from its purely physiological interest, knowledge of the 

 source of the carbon dioxid produced by this organism is of 

 scientific and practical importance in connection with the curing 

 of Cheddar cheese. Van Slyke and Hart (1903) showed that 

 carbon dioxid is given off from Cheddar cheese throughout the 

 curing process. The lactose of cheese, however, is entirely con- 

 sumed during the first few days; hence the source of the carbon 

 dioxid is not the sugar. The discovery by Miss Evans of the 

 occurrence of a gas-producing streptococcus in Cheddar cheese 

 naturally suggested that this organism might account for the 

 evolution of carbon dioxid from cheese of this type. In an effort 

 to throw some hght on this subject the work reported in this 

 paper was undertaken. 



' Published with the permission of the Secretary of Agriculture. 



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