168 SCIENCE AND PRACTICE OF DAIRYING. 



the cream formed during souring before using it, and discarding it if it 

 possess the slightest flavour. The quantity of sourer used should not 

 exceed at the most 5 per cent of the liquid to be soured. It is better to 

 use only 2 per cent, or even less, for cream, as it is only with cream it is 

 used, since milk which is to be churned is allowed to sour itself, and the 

 temperature of the cream should be raised somewhat during souring, 

 within the limits already mentioned. These limits, which are 16 to 

 20 C., must be rigorously maintained, since experience has shown that 

 the security of the manufacture is endangered if these limits be exceeded, 

 either above or below. There is no necessity to exceed these limits, since 

 the margin which they give, though apparently a narrow one, is sufficient 

 at every season of the year to regulate the temperature of the cream so 

 that it may safely ripen in from 18 to 24 hours. Ripening is either 

 hastened or retarded by bringing the temperature of the cream for a 

 shorter or longer period nearer to the higher or lower limit. By a diligent 

 and regular observation of the temperature of the souring of cream, by 

 frequently tasting it, and, above all, by carefully watching the progress 

 of the souring, an amount of knowledge and experience can be readily 

 gained by means of which successful work is secured much more surely 

 than by repeated and exact determination (chemical) of the lactic acid in 

 cream. By too little souring the yield suffers in quantity, but only to 

 a slight extent, while the quality is not at all impaired. On the other 

 hand, in the case of too much souring, a yield of good butter is impossible. 

 Especial care should be taken, therefore, that the cream is not allowed to 

 become too ripe that is, too sour. 



There are no practical experiments to show whether the cream-souring 

 effected by lactic fermentation can be replaced by artificial souring by 

 means of lactic or acetic acid. It is also very difficult by the latter means 

 to effect in an equable and perfect manner the ripening of the fluid to be 

 churned. That is best effected by lactic fermentation taking place equally 

 throughout the whole mass. If the butter possessed any blemish which 

 can be traced to the disturbed development of the souring of the cream, 

 pure cultures of lactic ferments should be at once obtained for souring 

 the Pasteurized cream, and such pure cultures should be used until it is 

 possible to again obtain a good sourer, by allowing the milk to become 

 spontaneously sour. Such pure cultures of lactic ferment can now be easily 

 obtained at the dairy experiment stations. By regularly Pasteurizing the 

 cream, the yield of a uniformly good butter is greatly promoted. 



91. Churning. The changes which take place in the churn 

 during churning, from the solidifying of the fat of the individual 

 fatty globules of the milk, to the appearance of the little lumps of 



