MILTON J. ROSENAU 400 



sugar, causing the brownish color; partial disarrangement of the normal emulsion, and 

 coalescence of some of the fat globules; coagulation of the serum albumin, which be- 

 gins at 167° F. ; the ferments are killed; some of the vitamins, notably C, are affected. 



Boiled milk has a cooked taste which appears at about 158° F. This is due per- 

 haps to the decomposition of certain of the proteins in the milk. The loss of certain 

 gases also alters the taste, so that milk heated in closed vessels has a less pronounced 

 flavor than if heated in open vessels. 



Milk heated in the open air forms a pellicle which renews if it is removed. This 

 scum forms when milk reaches about 140° F. It consists of: 



Per Cent 



Casein and albuminoid material So. 86 



Fatty matter 45-42 



Ash 3.72 



Milk heated in closed vessels does not form a pellicle, even when the temperature 

 reaches the boiling-point. It seems that this pellicle is due mainly to the drying of the 

 upper layer of the liquid. Heat causes a progressive decline in the H-ion concentra- 

 tion of the milk as the temperature rises. Evidently, the heat modifies the balance of 

 colloids in the milk. 



It is claimed that heat influences the availability of calcium and phosphorus of 

 the feeding mixture. It appears that the heat of pasteurization throws the calcium 

 salts more or less out of the solution, and thus they are made less readily available. 

 This does not occur to the same degree in quickly boiled milk, which therefore has 

 its advocates both here and abroad for infant feeding. 



Milk properly pasteurized at temperatures between 142° and 145° F. and then 

 cooled cannot be distinguished from raw milk by taste. Practical tests to determine 

 this point are convincing. 



CREAMING ABILITY OR CREAM VOLUME 



By "creaming ability" or "cream volume" is meant the amount of visible cream 

 which rises to the top of the milk on standing. No noticeable effect is produced upon 

 the cream volume when milk is heated up to 145° F. for thirty minutes. It is first 

 observed at about 146° F. and is of practical importance at i47°-i48° F. 



The creaming ability of milk is also influenced by the feed of cattle from which 

 the milk is obtained, the state of lactation of the dairy cow, the percentage of fat in 

 the milk, the size and grouping of the fat globules, the viscosity of the milk serum, the 

 temperature of the milk during creaming, recreaming of the milk, passing of the milk 

 through a separator, and remixing the cream and milk, and finally the agitation of 

 the milk. In the pasteurizing plant the creaming ability is affected by clarification, 

 agitation, cooling, and storing, as well as by the heat. 



GERMICIDAL PROPERTY OF MILK 



The germicidal property of milk has been much misunderstood. It is specific and 

 varies in different animals and even in the same animal at different seasons.' It is 

 destroyed at 167° F. (70° C.) for fifteen minutes, or between 176° and 194° F. (80°- 



' Chalmers: Brit. J. Exper. Path., 5, 271. 1924. 



