447 



CONDITIONS AFFECTING THE CHARACTER OF 

 BUTTER-FAT. 



Butter-fat, which belongs to the class of compounds known as 

 glycerides — that is, combinations of glycerin with certain acids- 

 is, like many other products of animal metabolism, a substance 

 of varying composition, and the nature and relative proportions 

 of its constituent glycerides are affected by a number of causes. 

 Thus they are dependent upon the idiosyncracy of the cow, the 

 changing conditions of its existence, the nature and amount of 

 its food, the period of lactation, &c, &c. As is well known, the 

 nervous organisation of the animal has also an important 

 influence on the milk secretion, but to what extent it affects 

 the proportion or character of the glycerides in the milk-fat 

 is not definitely made out. In fact, the precise influence of 

 all these agencies on the chemical composition of butter has 

 been very imperfectly studied, mainly by reason of the tedious 

 and imperfect nature of the analytical processes which are used 

 to isolate and determine the nature and amount of the con- 

 stituent glycerides. It has, however, been established that the 

 proportion of olein is greatest in the early period of lactation. 

 In some cases it may amount to as much as half the weight of 

 the fat. After a certain period the palmitin and stearin increase, 

 the amount of olein falling to less than half its maximum 

 quantity. These changes are apparently associated with the 

 variation in the size of the fat globules which occurs during the 

 lactation period. As the globules decrease in size the propor- 

 tion of olein also decreases, and the fat becomes harder and of 

 higher melting-point. 



During the last flve-and-twenty years a considerable body of 

 analytical evidence has been accumulated concerning the influ 

 ence of these factors of change upon certain physical and 

 chemical characteristics of butter-fat, from which a limited 

 number of important deductions are possible. This evidence 



