APPLICATIONS OF LACTIC ACID FERMENTATION 107 



example may be taken from Conn and Esten's investigations 1 . 

 Although the cream was hand-skimmed, it did not show a high 

 bacterial count to start with. It was allowed to stand at 20 to 

 21 C. 



From the accompanying table it is seen that the count increases 

 steadily during the first forty-eight hours, and even reaches to over 

 1,000 million bacteria per cubic centimetre, after which it decreases. 

 At first all the different groups of bacteria increase in numbers, 

 but later on the lactic acid bacteria gain the upper hand, and by 

 degrees suppress the other organisms. The most persistent seem 

 to be the pseudo lactic acid bacteria and the alkali-producing 

 bacteria (Bacterium lactis innocuum), the cream having been 

 particularly rich in the latter at the outset. 



Among the lactic acid bacteria, only the Streptococci multiply 

 at first, but after the count (lactose gelatine plates) has reached 

 the maximum, bacteria belonging to other groups gradually 

 appear and begin to suppress those present. At the same time, 

 yeast and Oidium lactis appear, as in milk. The period of the 

 maximum count, which always synchronises with the thickening 

 of the cream, is also the period of the purest lactic acid fermenta- 

 tion. If the cream becomes over-sour, the most beneficial of the 

 lactic acid bacteria will disappear and other microorganisms will 

 develop which may spoil the keeping qualities of the butter, but 

 which may, on the other hand, impart to it a stronger aroma. 

 It is difficult to fix any particular degree of acidity at which the 

 souring should be interrupted, for, as we shall see later, the degree 



1 " The Ripening of Cream," Storr's Agricultural Experiment Station 

 Report, 1900, p. 13. 



