552 COMPOSITION OF BUTTER. 



all the ingredients which exist in milli. It consists, however, essentinlly 

 of the fat of milk intimately mixed with a more or less considerable 

 proportion of casein and water, and with a small (luantity of sugar of 

 milk. Fresh butter is said to contain about one-sixtli of its weiglit (16 

 per cent.) of these latter substances, and five-sixths of pure fat (Chev- 

 reul). How much of the 16 per cent, usually consists of cheesy matter 

 has not yet been determined.* 



It is probable, however, that the proportion of cheesy matter contained 

 in butter varies very much. The thickness and richness of the milk— - 

 the mode of preparing the butter, whether from the whole milk or from 

 the cream — the way in wfjich the cream is se})arated from the milk, 

 whether by clouting or otherwise — and ths nature of the food and pas- 

 ture, must all affect in a very considerable degree the relative pro- 

 portions of the fatty and cheesy matters of which our domestic butter 

 consists. 



Besides the casein and sugar, butter also usually contains some colour- 

 ing substance derived from the plants on which the .cow has fed, and 

 some aromatic or other similar ingredients to wliich its peculiar flavour 

 is owing, and which are also derived from the food on which the animal 

 lives. 



The fat of butter may be readily separated from all these substances, 

 and obtained in a nearly pure state. Fresh newly-churned butter is 

 melted in a cylindrical jar at a temperature of 140° to 180° F., the 

 fluid oil poured off" into water heated to the same temperature, and re- 

 peatedly shaken with fresh portions as long as any thing soluble is taken 

 up. When left at rest in a warm place, the melted fat rises to the sur- 

 face in the form of a nearly colourless transparent oil, which, on cooling, 

 hardens into a colourless mass. 



This pure fat may be preserved for a much longer time without be- 

 coming rancid (Thenard). It is the various substances with which its 

 fatty matter is mixed that give to common butter its tendency to become 

 so speedily rancid and to acquire an unpleasant taste. To the nume- 

 rous precautions which have been adopted with the view of counteract- 

 ing this tendency, and of preserving the sweet taste of butter, I shall pre- 

 sently direct your attention. 



§ 11. Of the average ^quqnlity cf butter yielded by milk and cream, and 

 of the yearly yroduce of a cow. 



1 have already made you acquainted with some of those numerous 

 circumstances by which the quality of milk is affected. These same 

 circumstances will necessarily more or less affect the quantity of butter 

 also, which a given weight or measure of milk can be made to yield. 



Thus in the King William's town dairy (County Kerry), the average 

 quantity of milk and butter yielded by the Kerry and Ayrshire breeds 

 respectively was, in a whole year — 



Ayrshire cow, 1328 quarts, of which 9^ to Qf^ quarts gave 1 lb. of but- 

 ter. 



* Since the above was written, two samples of fresh butter, from cream, examined in my 

 laboralory, have yielded only 0-5 and 07 per cent, respectively of cheesy mutter. This is 

 certainly a much smaller quantity than I had expected. Does butter from the tchole milk 

 contain morel A series of such examinations would prove not iminteresting. 



