MILK 9 



and myristin make butterfat harder while olein and butyrin make it 

 softer. 



The churning temperature is largely determined by the relative 

 amounts of hard and soft fats; other conditions being the same, the harder 

 the fat the higher the churning temperature. The relative amounts of 

 hard and soft fats are influenced by: (1) the breed, (2) the feed, (3) the 

 period of lactation, and (4) the individuality of the cow. The butterfat 

 of Jerseys is harder than that of the Holsteins and therefore requires 

 a higher temperature about 6F. to churn. It is inherent in some cows 

 to produce a soft and in others a hard butterfat. With the advance of 

 the lactation period, the proportion of hard fat increases and churning 

 becomes difficult. By feeding certain fats the character of butterfat 

 may be affected. 



The soluble fats, of which butyrin is the most important, help to 

 impart to milk and cream their characteristic flavor. Butyrin is found 

 only in butterfat and so distinguishes it from vegetable and all other 

 animal fats. 



Recent investigations at the University of Wisconsin Agricultural 

 Experiment Station have demonstrated that there is an unknown sub- 

 stance in butterfat, in the fat of eggs and in the fat of certain organs 

 like the kidneys which is essential to young animals to make normal 

 growth, but which, as far as known, does not exist in plants or in body fat 

 in quantities large enough to satisfy them. This means that all fats 

 are not equally valuable to animals during growth and in the opinion of 

 McCollum, indicates that oleomargarine, since it contains a consider- 

 able admixture of the body fat of animals, is not equal in physiological 

 properties to an equal amount of butter, although it may possess as 

 much energy and equal digestibility. 



Proteins. Casein. Casein is the most important protein of milk 

 because it constitutes about 80 per cent, of all the proteins and because 

 its presence makes the manufacture of cheese and other products pos- 

 sible. It is held in colloidal suspension in the milk serum and is not pre- 

 cipitated therefrom by boiling. Pure casein is white and amorphous 

 and without taste or smell. Richmond considers it probable that casein 

 exists in milk as a calcium sodium salt combined with one molecular 

 proportion of tricalcium phosphate. In the souring of milk the lactic 

 acid combines with the calcium of this compound forming free casein 

 which on the formation of more acid takes up the acid without definite 

 chemical combination to make the curd of sour milk. Similar changes 

 occur when milk is treated with other acids, such as acetic, hydrochloric 

 or sulphuric. In this way casein is precipitated from skim-milk to be 

 manufactured into size, paints, combs and other things. Casein is 

 also precipitated in the slime of separator and of clarifier bowls. Dilute 

 solutions of the alkalies, such as caustic soda and ammonia, act upon 



