316 CITY MILK SUPPLY 



heaters, holders and retarders which yields its heat to the cold milk as it 

 flows over these sections and which is finally thoroughly cooled in passing 

 over the lower sections through which cold water or brine runs. These 

 regenerative coolers are economical and are commendable if they receive 

 proper care but they are to be condemned if they are not cleaned thor- 

 oughly and regularly for so, the milk in passing them is contaminated. 



In choosing a cooler, the quantity of milk to be handled, the tempera- 

 ture to which the milk is to be reduced and the suitability of the machine 

 for the plant should be considered. The capacity of the cooler is largely 

 determined by the area of cooling surface and by construction such that 

 a good circulation of the cooling medium can be maintained. The econo- 

 my of the circulation must also be considered for where water is scarce 

 or water rates high it may be an important item. 



With open coolers the temperature of the room wherein the cooling 

 is done has some effect. Thus in summer when the cooling is being done 

 with cold water it may be necessary to run the milk over the cooler twice 

 to reduce it to approximately the temperature of the water, when in win- 

 ter once would suffice. It is impracticable to reduce the temperature of 

 milk much below 50F. in summer without the use of ice or a refrigerating 

 machine. With ice water as the cooling medium, only with difficulty 

 can the milk be cooled much below 40F. while with brine, the tem- 

 perature may easily be brought down to 34F. In cooling milk, the 

 temperature should be taken occasionally with a good thermometer 

 to assure the operator that he is really getting good results. 



Many cities now require that open coolers be enclosed with a cover 

 to protect the milk as it flows over the cooler from contamination from the 

 air. This is regarded as of particular consequence in cities, where air 

 is likely to be sooty and dusty and more or less fecally polluted. Of more 

 importance is it to see that the cooler is perfectly clean and sterile before 

 any milk is run over it. Of course the cooler must be thoroughly cleaned 

 after each run but even when this has been properly attended to dust is 

 likely to have settled on the apparatus in the interim between the clean-up 

 and the time for the next run. Hence the need of thorough rinsing 

 and steaming before starting. Bacterial tests have shown that the first 

 milk over the cooler is apt to show a higher count than that which comes 

 over later, the explanation of which is, that the first milk washes off the 

 cooler. In pasteurizing plants the first milk from the machines is likely 

 to have a high bacterial count because they have not settled down to 

 uniform operation; therefore, this first milk should not be run over 

 the cooler to contaminate it, but should be returned for repasteurization. 



Filling the Bottles. As soon as milk is cooled it is put into cans and 

 removed to a cold room or it is bottled. Small dairymen fill their bottles 

 by hand with a filling dipper but this is a tedious job and those who 

 can afford something better use an inexpensive machine that enables 



