Production of Butter. 



39 



by which means it becomes converted into a ferment, which 

 has the property of slowly, in the first instance, converting the 

 sugar of the milk into alcohol, which latter, by further oxidation, 

 is converted into lactic acid, the lactic acid acting upon the coat- 

 ing of the fatty globules as previously noticed. This action in- 

 variably takes place during warm weatlier, the original fermenta- 

 tive action being somewhat similar to that of the mode of brew- 

 ing beer at a low temperature, as practised in Bavaria. Dr. 

 Lyon Playfair has, however, stated that in winter a different 

 action takes place, namely, that during cold weather the tempera- 

 ture is not sufficiently elevated to cause vinous fermentation, and 

 that the action of the oxygen in the first instance, at this season, 

 is confined to the casein, in other words the putrefactive fer- 

 mentation takes place. It is impossible, therefore, to make good 

 butter from milk undergoing such a change as is here named, for 

 when incipient putrefaction has once commenced, it cannot be 

 arrested by ordinary means, and is consequently imparted to the 

 minute quantity of casein remaining in the butter, and is never 

 vrholly extracted ; such butter speedily becomes rancid, even in 

 winter, notwithstanding the low temperature of that season is 

 unfavourable to the promotion of putrefactive changes. 



The reason why sweet cream requires less churning than cream 

 and milk mixed, arises from the circumstance that in cream alone 

 the absorption of oxygen, which takes place at every agitation, is 

 diffused throughout a much smaller quantity of liquid, the lactic 

 acid formed is consequently much more concentrated, and acts 

 with greater energy on the outer coating of the butter globules ; 

 butter, therefore, comes more quickly. It must be observed that, 

 however sweet the cream may be, when placed in the churn, 

 butter is never formed until after the formation of lactic acid. In 

 making butter, sweet cream is a relative, rather than an absolute 

 term, for in fact acescency commences within a few hours after the 

 milk has been set to stand. In endeavouring to obtain butter 

 from sweet milk alone, the labour required to form the butter is 

 excessive, for in this instance the quantity of oxygen that can be 

 absorbed through the influence of agitation is proportionally de- 

 creased in the ratio of the increased quantity of liquid throughout 

 which the butter is diffused ; whilst, at the same time, a larger 

 amount of oxygen is required in order to convert a portion of the 

 sugar of milk into alcohol, and ultimately into lactic acid. But in 

 a closed churn a long time elapses before these changes take 

 place : consequently, we need not be surprised to find that Dr. 

 Traill and others failed to obtain butter from sweet milk alone ; 

 yet on one occasion the experiment was tried in Carlow, butter 

 was obtained from new milk under the inspection of the writer, 

 but it took upwards of five hours to produce it, and the butter 



