Pasteurization of Milk 



7 



allowed for any fluctuation above the 

 minimum points that may be required 

 in commercial practice. There are 

 many other factors other than temper- 

 ature and time requirements that enter 

 into the problem of the efficient pas- 

 teurization of milk which are disctissed 

 under other subjects in this report. 



V. The Mechanical Features and 

 THE Operation of Pasteuriz- 

 ing Plants. 

 The material included under this 

 subject is limited to pasteurizing ap- 

 paratus and its operation ; the matter 

 of the building, and of can fillers and 

 cans, bottle fillers and bottles, can 

 washers, bottle washers, sterilizers, 

 cap sterilizers, bottle inspection, cap 

 storage, etc., forming important parts 

 ' of milk pasteurization, are not consid- 

 ered. Owing to the wide range of ca- 

 pacities and importance of local condi- 

 tions, it is impossible to make any 

 specific lay-out that would apply to 

 even a majority of pasteurizing plants. 

 There are, however, certain general 

 conditions that apply to all plants and 

 all plant operation, to all pasteurizing 

 apparatus and the machinery co-ordi- 

 nating therewith, to the sterilization 

 of containers, to the treatment of the 

 milk, and to the handling of the milk 

 after treatment, in order that the out- 

 put of the plant may be entitled to be 

 sold under the marking or label of 



"PASTEURIZED." 



(1) Methods of Pasteurization. 

 Milk may be pastuerized in the bottle 

 or have the treatment applied by 

 means of apparatus, which may be of 

 what is known as the batch or inter- 

 mittent type, or as the open or closed 

 continuous type. The apparatus gen- 

 erally used for applying the pasteuriza- 

 tion treatment is either of the vat 

 type, that is, (a) a vat in which the 

 milk is heated, held and cooled, or (b) 

 a combination of a heater, a vat oii 

 series of vats for holding the milk 



static and a cooler, or (c) a combina- 

 tion of a heater, a series of vats for 

 holding the milk flowing and a cooler, 



In any of the above mentioned types 

 of apparatus the treatment may be ap- 

 plied, and pasteurization effected by a 

 competent operator, providing the ap- 

 paratus is free from inherently danger- 

 ous defects. 



It is entirely practical to construct 

 the intermittent or continuous type of 

 pasteurizing apparatus so that every 

 drop of milk and every particle of foam 

 developed by the movement of the 

 milk will have passed through the 

 complete course of the apparatus, and 

 that when milk is supplied to such an 

 apparatus at the proper volume per 

 time period, and the necessary tem- 

 perature maintained, the milk delivered 

 from the discharge outlet will have had 

 pasteurizing treatment. 



,(2) Pasteurization in the Bottle. 

 Milk that is pasteurized in the bottle 

 must have the full minimum treatment 

 applied, and care must be used in tak- 

 ing the milk temperature so that the 

 instrument is not affected by the hot 

 milk at the top of the bottle, or by the 

 heating medium. The time of the 

 holding period does not start until all 

 of the milk in all the bottles is at the 

 minimum temperature. This temper- 

 ature must not be lowered until the 

 end of the holding period, and the hold- 

 ing period must not be shortened. If 

 any temperature recording instrument 

 is used, care must be taken to see that 

 the heat of the apparatus does not 

 cause a higher reading than the actual 

 temperature of the milk. If water is 

 used in cooling, care must be taken tb 

 prevent it from being drawn into the 

 bottle by the contraction of the milk. 

 Bottles used for milk to be treated 

 therein must be washed and sterilized 

 before being filled with milk, as the 

 pasteurizing temperature is not suffi- 

 cient to sterilize the bottles that have 

 been returned to a milk plant, often 



