A STUDY OF THE STREPTOCOCCI CONCERNED IN 

 CHEESE RIPENING 



By Alice C. Evans ^ 



Dairy Bacteriologist, Dairy Division, Bureau of Animal Industry, United States Depart- 

 ment of Agriculture 



INTRODUCTION 



In a general way streptococci may be divided into three groups: 

 First, the pathogenic streptococci, which differ among themselves in 

 virulence and in their predilection for certain organs, as well as in certain 

 biochemical reactions. Second, those streptococci which are common 

 in the udder, in the saliva, and in the intestines. These, so far as we 

 know, differ from the first group chiefly in their lack of virulence. 

 Third, the milk-souring streptococci (Streptococcus lacticus). 



It is the purpose of this paper to present streptococci in another 

 role — viz, as the producers of flavor substances and other ripening 

 changes in food prepared for consumption by fermentation, and par- 

 ticularly in the ripening of cheese. In this connection the streptococci 

 are important as one of the factors concerned in rendering palatable 

 many articles of food in use throughout the world. But they are 

 unobtrusive, and demand little attention — only that the proper condi- 

 tions for their growth shall be provided. The manufacturer of the 

 food meets this demand without knowing why; he only knows that if 

 he follows such and such a procedure he will obtain the desired results. 

 Therefore the flavor-producing streptococci have escaped notice. 



Streptococci from all four of the sources mentioned differ so slightly 

 that there has been much discussion as to whether they are varieties 

 of the same species. Several species, however, all belonging to the genus 

 Streptococcus, have come to be generally recognized. The accepted 

 definition of the genus as given by the Winslows {23, p. 141Y is as 

 follows : 



Parasites. Cells normally in short or long chains (under unfavorable cultural 

 conditions, sometimes in pairs and small groups, never in large packets). Generally 

 stain by Gram . On agar streak , effused translucent growth , often with isolated colonies. 

 In stab culture, little surface growth. Sugars fermented with formation of large 

 amount of acid. Generally fail to liquefy gelatin or reduce nitrates. 



• The writer is indebted to her collaborators in the Dairy Division for hearty cooperation whenever the 

 investigation was found to extend into the special field of research of any one of them. The gas analyses 

 were made by Dr. W. M. Clark; Dr. J. N. Currie made the volatile-acid determinations; Mr. H. C. Jordan 

 made the experimental cheese of the Cheddar type; and Mr. K. J. Matheson and Mr. F. R. Cammack made 

 the soft-cream cheese. 



2 Reference is made by number (italic) to " Literature cited, " p. 251-252. 



Journal of Agricultural Research, Vol. XHI, No. 4 



Washington, D. C. April 22, 1918 



mv (235) KeyNcA-iS 



