196 PRACTICAL DAIRY BACTERIOLOGY 



changes which considerably modify its nature. 1 The lactic 

 acid bacteria always develop lactic acid, and the cream becomes 

 sour; but there are other changes also. We do not yet know 

 what all these changes are nor to what extent they contribute 

 to the ripening phenomenon. That the other changes have 

 something to do with the production of the flavor in butter is 

 evident from the fact that a butter flavor cannot be produced 

 in the cream by adding lactic acid to it, and if the ripening were 

 wholly the result of the souring, the addition of lactic acid 

 should produce the same result as normal ripening. 



Growth of Bacteria During the Ripening. The study of the 

 growth of bacteria during the ripening of cream is quite sug- 

 gestive and instructive. At the outset the cream is quite cer- 

 tain to contain numerous kinds of bacteria, differing much, of 

 course, in different samples. In the composite cream of a cream- 

 ery the varieties will be very numerous, while in cream of a 

 private dairy they may be less numerous. During the ripening 

 the cream is commonly kept between 60 and 70, at which 

 temperature many bacteria develop rapidly, but not all kinds 

 with equal vigor. During the first few hours of the ripening 

 there is found to be a general increase in the number of bacteria 

 of nearly all kinds that were present in the original cream, so 

 that after six or eight hours there will almost universally be 

 found higher numbers of all species of bacteria than were 

 found at first. During this time, however, the lactic acid bac- 

 teria, especially of the Bact. lactis acidi type, have been in- 

 creasing more rapidly than the others. 2 In the very fresh 

 cream these bacteria may have been, and commonly are, com- 



1 Conn. Ann. Rep. Storrs Exper. Sta., 1890, pp. 91, 93 and 94. 

 Conn. Cent. f. Bact., II., ii., p. 409, 1896. Ill, p. 177, 1897. 

 Conn and Esten. Cent. f. Bact., II., vii., p. 743, 1901. 



Conn and Esten. Ann. Rep. Storrs Exper. Sta., 1900, 1901. 



Storch. Cent. f. Agr. Chem., 1891. 



Haywood and McDonnell, Bui. 44 Penn. State Col. Exper. Sta., 1899. 



2 Conn. Bacteria in Milk and Its Products. P. Blakistons Son, 1903. 

 Conn and Esten. Ann. Rep. Storrs Exper. Sta., 1901. 



