Principles of Milk Preservation. Ill 



reservoir that is filled with milk and surrounded with an 

 outer shell that contains the heating agent, steam or hot 

 water. 



Some of this class are provided with an agitator in the 

 milk reservoir so as to hasten the equalization of tem- 

 perature in the inner chamber, and at the same time keep 

 the milk in motion in order to prevent the coagulation of 

 the proteids. 



Most of them are arranged for a continuous delivery, 

 the milk flowing in at the lower end and displacing that 

 already pasteurized, which flows out above into a cooler. 

 In some of them the agitator even mixes the fresh supply 

 with that which has already been heated, so that the effi- 

 ciency of the process where milk is being treated for 

 direct consumption, is much lessened. 



Where it is constructed for continuous delivery, the 

 length of exposure must necessarily be quite limited, and 

 as the temperature of the milk ought not to exceed 160 

 F. for fear of scalding, it very often happens that the 

 pasteurizing process is not efficient. In the case of the 

 sour milk organisms, from the hygienic standpoint, it is 

 of little moment, but to insure absolute freedom from 

 disease germs, the temperature and the time of exposure 

 must be thoroughly under control. Very few of the ma- 

 chines intended for this purpose have been subjected to 

 a rigid bacteriological test, and the lack of this has allowed 

 the introduction of many designs that may be adapted 

 for the pasteurization of by-products intended for animal 

 food, for which purpose many of them were originally 

 designed, but they certainly do not deliver a product that 

 can be relied upon for human food. 



111. Intermittent pasteurizers. Inasmuch as the 

 biological and physical requirements as to pasteurizing, 

 necessitate milk being heated between the temperatures 



