562 MANUAL OF MILK PRODUCTS 



the separator, for other reasons, requires more attention on the 

 part of the operator when hot milk is skimmed than when 

 skimming is done at the usual temperature. 



The regenerative pasteurizers now on the market are both 

 economical and efficient for this purpose and will undoubtedly 

 give excellent satisfaction as milk heaters which pasteurize 

 both the skim-milk and cream by pasteurizing the whole milk 

 before skimming it. 

 Delivery of hot skim-milk. 



Pasteurized milk, when cooled to near 50 F. immediately 

 after heating, will keep sweet for a longer time than when allowed 

 to cool gradually. Experiments have shown that pasteurized 

 skim-milk when cooled at the creamery and delivered cold to 

 the patrons will not keep sweet so long as when delivered hot. 

 This is because the cans have not been sterilized after the milk 

 is delivered at the factory ; the milk left in the empty cans is 

 sufficient to start fermentations in the cooled pasteurized skim- 

 milk, no matter how thoroughly this has been pasteurized. 



If the skim-milk is delivered to the patrons while hot, the 

 rinsings of milk left in the cans are pasteurized by this hot 

 skirn-milk, and if it is then cooled to near 50 F. soon after heating 

 it will keep sweet a much longer time than raw skim-milk. 

 Cooling the cans of hot skim-milk without delay at the farm is 

 an important factor in keeping the milk sweet. It is not suffi- 

 cient to set the cans of hot skim-milk in a small tub of cold 

 water at the farm, as this small quantity of water is warmed 

 by the hot milk and, unless the water is changed often enough 

 to complete the cooling, the results are unsatisfactory. 

 The whole milk must be sweet. 



In order successfully to pasteurize skim-milk, the whole 

 milk from which it is skimmed must be perfectly sweet ; slightly 

 sour milk is curdled by heat and will clog the pipes through 

 which it passes. 



When skim-milk is pasteurized, the transportation cans are 



