TESTING OF MILK AND CREAM 89 



Some of these fats are known as hard and some 

 as soft. 



Palmitin and stearin are white, and are hard at 

 the ordinary temperature and melting at a tempera- 

 ture of 146 F. 



Olein makes up nearly 40 % of the weight 

 of butter, and it differs from the others in that 

 it begins to melt at the ordinary temperature, 

 and is not hard unless in very cold weather or in 

 the presence of ice. It has the property of melting 

 the other fats, which accounts for the oily ap- 

 pearance of butter should the day be slightly 

 warmer than usual. The larger the percentage 

 of olein present in milk fat the softer will the 

 butter be. 



Butyrin is the characteristic part of milk fat, 

 its presence or absence being the distinguishing 

 point between pure butter or margarine. When 

 this fat decomposes it sets free butyric acid, which 

 has a rancid smell. The rancidity sometimes 

 present in butter is due to its being set free. When 

 the fats in milk decompose fatty acids are set free, 

 which, being present in butter to the extent of 

 8 %, may be driven off in a current of steam. 

 They are then said to be volatile. The amount 

 of volatile fatty acid which may be set free 

 from margarine is very low indeed, because animal 

 and vegetable oil used in its manufacture contains 

 no butyrin. 



