108 Dairy Bacteriology. 



cover with a cloth or tin cover and allow the whole to 

 stand for half an hour. 



4. Remove bottles of milk and cool them as rapidly 

 as possible without danger to bottles and store in a re- 

 frigerator. 



109. Apparatus for commercial pasteurizing 1 . 

 Pasteurizing as applied to the preservation of milk, orig- 

 inated in Germany and Denmark, where it is used largely 

 in the treatment of skim-milk, and the heating of cream 

 in butter- making; The type of machinery that has been 

 devised for this purpose has therefore naturally been con- 

 structed on somewhat different principles than would 

 have been employed where milk is treated for direct con- 

 sumption. For the treatment of milk for direct con- 

 sumption, it is believed that the sanitary phase of the 

 problem demands more attention than the economic oper- 

 ation of the apparatus, and, therefore, it is more neces- 

 sary to use a machine that pasteurizes so thoroughly that 

 all possible disease bacteria are destroyed, than it is to 

 secure apparatus that will permit of the handling of large 

 quantities of milk. Pasteurizing involves considerable 

 time and trouble, and it is better not to have the process 

 done at all than to have it imperfectly performed. 



The various types of machinery that have been sug- 

 gested for this use may be grouped as follows, depending 

 upon their method of operation 1 . 



1. Continuous flow machines. 



2. Intermittent machines. 



110. Continuous flow pasteurizers. Apparatus of 

 this class varies much in detail, but they possess this 

 common principle that the milk enters the machine in a 



1 For the detailed description of pasteurizing machinery, reference 

 should be made to Monrad's Pasteurization of Milk, or Weigmann's 

 Conservierung der Milch. 



