Bacteria and Butter- Making. 139 



rington alkaline tablet, which permits of an accurate and 

 rapid estimation of the acidity in the ripening cream. The 

 amount of acidity to be produced must of necessity be gov- 

 erned by the amount of butter-fat present, for the forma- 

 tion of acid is confined to the serum of the cream; conse- 

 quently, a rich cream would show less acid by titration 

 than a thinner cream, and still contain really as much acid 

 as the other. The importance of this factor is evident in 

 gathered-cream factories. 



The rate of ripening is dependent upon the conditions 

 that affect the rate of growth of bacterial life, such as time 

 and temperature, number of organisms in cream and also 

 the per cent of butter fat in the cream. Some years ago 

 it was customary to ripen cream at about 50 to 60 F., 

 but more recently better results have been obtained, it is 

 claimed, where the ripening temperature is increased and 

 the period of ripening lessened. As high a temperature 

 as TO to 75 F. has been recommended. It should be said 

 that this variation in practice may have a valid scientific 

 foundation, for the temperature of the ripening cream is un- 

 doubtedly the most potent factor in determining what 

 kind of bacteria will develop most luxuriantly. It is well 

 known that those forms that are capable of producing bit- 

 ter flavors are able to thrive better at a lower temperature 

 than some of the desirable ripening species. 



The importance of this factor would be lessened where 

 a pure culture was used in pasteurized cream, because here 

 practically the selected organism alone controls the field. 



It is frequently asserted that better results are obtained 

 by stirring the cream and so exposing it to the air as much 

 as possible. Experiments made at the Ontario Agricul- 

 tural College, however, show practically no difference in 



