204 ELEMENTAHY AGRICULTURAL CHEMISTRY 



burn knock against each other or against other fat globules 

 and cohere. Portions of the aqueous liquid, butter-milk, are 

 enclosed in the masses of fat. During the *' working" of the 

 butter the butter-milk is more and more pressed out. 



The best temperature for churning depends upon the melting- 

 point of the fat in the particular sample of cream churned^ 

 Thus when cotton-cake has been used as food for the cows the 

 melting-point of the butter-fat is raised, and churning should 

 be done at a higher temperature. So, too, with " ripened " or 

 sour cream a slightly higher temperature than with sweet 

 cream is suitable. From 8° to 18° C. (4G° to 65° F.) is the 

 greatest range usually employed, and in most cases from 10° 

 to 15-5° C. is chosen (50° to 60° F.). Churning takes place 

 more readily at the higher temperature, but the resulting 

 butter will not be so free from casein nor the butter-milk 

 so free from fat as when the operation is done at a lower 

 temperature. 



Freshly separated cream is sometimes churned, but it is 

 generally admitted that the best flavour and aroma in butter 

 can only be obtained by the use of properly ripened cream — i.e., 

 cream to which the lactic organisms have either gained access 

 spontaneously or, as is preferred in modern practice, have 

 been added in the form of a " starter " of sour skimmed milk 

 or some pure culture of the lactic organisms. The degree 

 of " ripeness " which is probably best corresponds to about 

 0*5 per cent, of lactic acid ; but the acidity most suitable 

 depends to some extent upon the flavour desired in the butter. 

 If the cream be over-ripe the casein present may be com- 

 pletely coagulated, and on churning is found as white specks 

 or flakes in the butter, thus spoiling its appearance, and also 

 rendering it liable to contract unpleasant flavours and rancidity 

 on keeping. 



Salt is usually added to butter, serving both as a condiment 

 and as a preservative, the proportion varying from a mere 

 trace up to 6 or 7 per cent. 



Composition of Butter. — The main constituent is, of course, 



