42 PROPERTIES OF MILK 



so small a quantity that it cannot be determined quantitatively, 

 but only qualitatively. 



A very sensitive and reliable test for determination of the 

 efficiency of pasteurization was invented by Storch a number 

 of years ago. This is fully described in Chapter XV on 

 " Pasteurization." 



7. Divides the Clusters of Fat-globules. The fat-globules in 

 normal milk are grouped in minute clusters. When milk is 

 heated, these clusters break up, and each globule exists more or 

 less independently. When heated to an excessively high tem- 

 perature, and exposed to this temperature very long, the fat- 

 globules tend to run together. This can be proved by heating 

 milk in an open vat for about half an hour. A small amount of 

 yellow fat will then be seen floating on the top. 



8. Caramelizes the Sugar. The brownish color which the 

 milk assumes when it is heated excessively is due to a change which 

 the milk-sugar undergoes. Fleischmann claims that the sugar 

 begins to change into a substance known as lacto-caramel at a 

 temperature of 160 F. This change, however, is not pro- 

 nounced enough to be apparent in the color, unless the milk 

 is heated a long time. The higher the temperature is, and the 

 longer the milk is exposed to the heat, the more pronounced is 

 the change. 



General Remarks. While all of the above changes have 

 been found by investigators to take place when milk is heated, 

 they can, in a measure, be avoided, if special precautions are 

 taken in the heating and cooling with the special, recently 

 improved forms of apparatus for these purposes. 



The present common practice of heating milk, for consump- 

 tion as such, to 145 F., and holding at this temperature for 

 twenty to thirty minutes, is accomplished without materially 

 changing its chemical or physical properties, or imparting to it a 

 flavor that is at all objectionable. 



