THE DAIRY. 8 1 



ferments out of milk, but they can be held within reasonable 

 limits by absolute cleanliness and low temperature. Whilst 

 milk is warm, say at a temperature of 70 up to 100 Fahr., 

 their action is vigorous and their multiplication rapid. But 

 at 50 they are not very active, and at freezing-point they 

 are absolutely inert. When milk is drawn from the udder of 

 the cow it is at a temperature most favourable to the growth 

 and activity of these organisms : at 20 degrees above or 

 below that temperature the conditions are less favourable, 

 especially below it ; and while freezing renders them inert, 

 boiling destroys them. 



These microbes, however, are not implacable enemies in the 

 dairy ; properly controlled, they may be regarded as friends. It 

 is in milk that they are most of all troublesome, for it contains 

 in addition to copious moisture, the nitrogenous food, casein, 

 in which they flourish. But in cream, which contains but a 

 small proportion of casein, they serve the useful purpose of 

 developing the flavour of the butter, providing the cream be 

 held at a temperature which keeps them but moderately active, 

 or it be churned before they have had time to produce flavours 

 which are disagreeable. The pleasant flavour of butter is 

 developed by incipient decomposition, while advanced decom- 

 position destroys it. The "ripening" of cream is simply 

 the action of bacteria, and an advanced stage of ripening is 

 sourness ; the one improves, and the other degrades, the flavour 

 of the butter. 



It will now be seen how important are cleanliness and 

 temperature in dairy work, and in that department of it known 

 as butter-making, how necessary it is that cream should ripen 

 but not become very sour. Indeed, it should not be allowed 

 to become distinctly and obviously sour at all. 



The action of these microbes in cheese is also useful and 

 even necessary. As the cheese ripens, they become the fer- 

 ment which acts upon the casein, rendering it partially soluble 

 and developing the flavour which makes a properly ripened 

 cheese so attractive an article of food. It is the casein and the 

 butter in cheese which make it valuable as a food, but the 



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