136 Dairy Bacteriology. 



1. Vigorous growth in milk at ordinary ripening tem- 

 peratures. 



2 . Ability to form acid so as to facilitate churning and 

 increase the yield of butter. 



3. Able to produce a clean flavor and desirable aroma. 



4. Impart a good keeping quality to butter. 



5. Not easily modified in its flavor- producing qualities 

 by artificial cultivation. 



These different conditions are difficult to attain, for the 

 reason that some of them seem to be in part incompat- 

 able. Weigmann 1 found that a good aroma was gener- 

 ally an evanescent property, and therefore, opposed to 

 good keeping quality. Conn has shown that the functions 

 of acid-formation, flavor and aroma production are not 

 necessarily related, and therefore, the chances of finding 

 a single organism that possesses all the desirable at- 

 tributes are not very good. It may well be asked if the 

 conditions are so peculiar, how is it that a good product 

 is ever made where no special attention is given this 

 matter of culture starters? The reason for this is that 

 the ripening of cream is not a single type of fermentation, 

 but a complex process in which various organisms may 

 participate. 



In all probability no one germ possesses all of the de- 

 sirable qualities, but the resultant of the action of several 

 forms may produce a good product 2 . This idea has led 

 to the attempt of mixing selected organisms that have 

 been chosen on account of certain favorable characteris- 

 tics which they might possess. The difficulty of main- 

 taining such a composite culture in its correct proportions 

 when it is being propagated in the creamery is seemingly 

 well nigh insuperable, as one organism is very apt to 

 develop more or less rapidly than the other. 



1 Weigmann, Landw. Woch. f. Schl. Hoi., No. 2, 1890. 



2 Weigmann, Cent. f. Bakt., II. Abt., 3: 497, 1897. 



