294 CITY MILK SUPPLY 



duction in the bacterial numbers during the cooling period, especially 

 when the raw milk contained large numbers of bacteria before pasteuriza- 

 tion. As the experiments indicate that pasteurized milk can be cooled 

 on a commercial scale from 145F. to 50F. by forced air within 3 hr. 

 the process can be completed well within the 5-hr, limit. It is empha- 

 sized that the cooling of milk is absolutely necessary and that this proc- 

 ess does not eliminate cooling; it merely cools more slowly than is at 

 present customary. 7. So far as could be determined from experiments 

 conducted on this scale, the cream line and flavor of the milk are not in- 

 jured by this process. 8. These experiments indicate that it is commer- 

 cially practicable to cool hot pasteurized milk in containers not larger 

 than quart bottles by forcing cold air downward over them, when the 

 air is at 40F. or lower. 



On account of overheating portions of the milk, the process of pas- 

 teurizing milk in bottles by forcing hot air over them seems commercially 

 impracticable. 



Objections that have been raised to bottling milk hot are that the 

 air space that is formed in the bottle by the contraction of the milk in 

 cooling both makes the package unattractive to the consumer and gives 

 opportunity for the milk to churn as it is carried about in the delivery 

 wagons. 



Holders. Holders are of two principal sorts, namely; the absolute or 

 positive and the continuous holders or retarders. In the absolute hold- 

 ers the heated milk is actually held in insulated or jacketed tanks or com- 

 partments for a definite period of time, usually 20 to 45 min. and at the 

 pasteurizing temperature. They are very efficient, provided all the milk 

 is held the full time, and provided the temperature is maintained. In 

 some holders of this class scum formation is excessive and impairs their 

 effectiveness because the foam is considerably cooler than the milk and 

 so the contained germs escape destruction. Excessive foam formation 

 greatly increases the surface of the exposed milk, consequently the evap- 

 oration therefrom causes undue shrinkage in the milk. 



Holders of the absolute type : 



1. The combined heating, holding and cooling tanks described as 

 type 6, under heaters. 



2. A tank divided into compartments each of which has at the bottom 

 an outlet valve that is operated by an arm connected to a center shaft 

 that passes up through the machine and makes one revolution in 30 min. 

 At the top of the shaft is a distributing trough that fills the compartments. 

 The emptying device is so arranged that six of the compartments are full 

 at a time, while of the two others one is being emptied and the other 

 filled. In this way a compartment after being filled with hot milk is 

 held for 30 min. after which it is automatically emptied. The compart- 

 ments are arranged so that when the machine is going at full capacity 



