11 



PRESERVING BY PASTEURIZING. 



While the heating of milk to boiling point, or there about, always 

 gives a boiled flavor, it is possible to reduce this so as to make it 

 barely perceptible, by heating only to 150 to 155 Fah. 



Experiments have shown that if the milk is kept at this temper- 

 ature for 20 to 30 minutes most of the bacteria will be killed. 



First of all the lactic acid bacteria will succumb and this is the 

 fellow which generally " loppers " the milk. 



But other and more dangerous bacteria among those which are 

 most liable to be found, are also killed. 



Thus did "BITTER" find that 30 minutes at 155 killed the 

 tubercle, the typhoid and the cholera baccillus. 



But there are also others which require a temperature of 230 

 and more to destroy and it is thus evident that a perfect safeguard 

 is not even obtained by heating to 212 or 215. 



And if this is so, it seems to me absurd to attempt to overcome 

 the popular prejudice against the "boiled flavor' 1 when we can 

 secure a safeguard against the most common dangers by heating 

 only to 155 which does not develop that flavor. 



But. while heating to boiling point and even heating to 155 

 kills most of the bacteria, it does not kill their spores, and hence 

 if the milk is left at a favorable temperature (between 80 and 100) 

 for any length of time, the genus will develop and the battle com- 

 mence anew. 



The milk must therefore be cooled immediately as low down as 

 possible, at least to 50, and it is of the highest importance that this 

 is done quickly, especially between the temperature of 120 and 70. 

 It matters less if the cooling is slow from 155 to 120. 



INTERMITTENT PASTEURIZATION. 



In view of the above fact, it has been proposed by Dahl to heat 

 the milk inclosed in vessels to 158 f or | hour, then cool to 104 for 

 the same time, then heat again and cool, in all four times At last 

 heat it to 175 or 212 for half an hour and cool to 55. 



This is however neither sterilizing nor pasteurizing and is sim- 

 a modification of the intermittent sterilization proposed by Tyndall, 

 and though very effective it is very complicated and expensive. 

 Large quantities of milk has nevertheless been shipped to London 

 from Norway, preserved by this %i DAHL " method. 



