186 THE MILK QUESTION 



milk, therefore, spoils just as raw (that is, unheated) milk 

 spoils. Pasteurization does not mean simply the heating 

 of milk, for the subsequent rapid cooling is a very impor- 

 tant part of the process. If heated milk is allowed to cool 

 slowly it remains at a temperature between 20 and 37 

 C. for a very long time. This is the best temperature for 

 the development of bacteria and their poisonous products. 

 It requires but a few hours under such conditions to de- 

 velop an enormous brood of bacteria. 



Sterilization means the destruction of all microscopic 

 life that may be in or on an object. Even boiling will not 

 sterilize milk, because some of the hardy spores resist the 

 boiling temperature. Milk that has simply been boiled 

 will, therefore, spoil and decompose in a particularly un- 

 desirable way; that is, it putrefies, rather than ferments. 

 Putrid milk is alkaline and apt to be poisonous : fermented 

 milk is acid and sours normally. To sterilize milk it is 

 necessary to heat it at a temperature of 120 C. for fifteen 

 minutes, or to boil it for hah* an hour on three successive 

 days. The reason for this is that the spores which escape 

 the first boiling germinate in the milk and are destroyed at 

 the second boiling. Two boilings may be enough, but a third 

 is occasionally necessary. A flask of sterilized milk, if pro- 

 tected from re-contamination and kept from evaporation, 

 will remain unchanged indefinitely. 



Much confusion has arisen from a failure to understand 

 the difference between sterilized milk and pasteurized milk. 

 Many of the undesirable properties of boiled milk, or milk 

 heated to a high temperature, do not apply to milk pas- 

 teurized at the lower temperatures, which modern research 

 has shown to be sufficient. 



Historical 



Pasteur in 1860 to 1864 studied the diseases of wine and 

 found that it was sufficient to heat wine for a few moments 

 at a temperature of from 50 to 60 C. in order to prevent 



