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The ripening of cream for the churu is a process which 

 requires time and heat in definite ratios. That is, thirty- 

 six hours and sixty degrees of temperature are required 

 to bring the cream skimmed from perfectly sweet milk to 

 ithe right stage of acidity for churning. If the milk has 

 been kept for twelve hours after it has -turned distinctly 

 'sour, twenty-four hours will be enough for the perfect 

 ripening of the cream for the churn. If kept longer 

 than this, yiscosity is produced, and this is one of the 

 early stages of that final decomposition of the milk which 

 produces the disagreeable flavors of butter arising from 

 the formation of essential oils. These oils result from the 

 decomposition of, first, the lactic acid, and, second, that 

 of the caseine which may remain in the butter. These 

 changes will be more particularly described when we 

 come to consider the nature of butter. But as this 

 viscosity in the cream is the germ, as it were, by which 

 the changes are set in progress, its production is to be 

 avoided most assiduously. 



The right stage of cream for churning is when acid 

 is perceptible, and an agreeable aromatic odor is given 

 off from the cream jar. This is reached at the instant 

 when the lactic acid begins to break up into butjTic acid 

 by a simple chemical combination. This is brought 

 about by the effect of the caseine which has previously 

 changed the milk sugar into milk (lactic) acid and now 

 still further acts upon this acid to transform it. Such 

 action is accompanied by a fermentation in which car- 

 bonic acid and hydrogen with some water are evolved and 

 escape from the cream, and one and a half atoms of lactic 

 acid are wholly decomposed and give off this carbonic 

 acid and water, hydrogen requiring twelve atoms of 

 oxygen to effect the change. This oxygen is taken 

 from four other atoms of lactic acid, which is by this 

 deprivation converted into three atoms of butyric acid, 

 the substance that gives the aroma to butter made 



