STERILIZATION OF MILK 21 3 



In a mechanical refrigerator milk can be kept longer 

 than in an ice chest. The temperature close to the cooling 

 coil in such a refrigerator is only a degree or two above 

 freezing, so low as to prevent the growth of practically all 

 bacteria. Milk can retain its fresh taste seven days or more 

 under such circumstances, although it is not well to make 

 a practice of keeping it that long, as it may no longer be 

 safe to drink even though it is imchanged in flavor and 

 appearance. 



4. Use of Preservatives. The facts given elsewhere con- 

 cerning the use of preservatives apply equally in the case 

 of milk. The use of any preservative is always to be dep- 

 recated, and, so far as concerns the housewife, the rule 

 should be that no preservatives should ever under any 

 circumstances be used in milk. 



It should be borne in mind that none of these devices 

 remove dangerous disease germs. They make it possible 

 to keep the milk longer, but do not make it more whole- 

 some if it chances at the outset to contain any harmful 

 bacteria. 



5. Preservation of Milk by Heat. Long before modern 

 bacteriology had explained the reasons for it, heat had 

 been used for keeping milk; and physicians had long 

 recommended the boiling of milk which invalids were to 

 drink, though they did not understand that the reason for 

 the heat was that it destroyed bacteria. In the use of heat 

 for this purpose two different methods may be mentioned. 



(a) Sterilization. By sterihzation, strictly speaking, is 

 meant the application of sufficient heat to kill all bacteria 

 present in the milk. This can be done only by the use of 

 temperatures above boiUng, by methods beyond the reach 



