198 STATE BOARD OF AGRICULTURE. 



ature. Oh the other hand, it simply retards their growth while they are 

 under the influence of the cold only, for when they are transferred to a 

 warm temperature they grow as readily as those bacteria which have 

 been kept at a warm temperature for some time. 



When we take milk from the cow and put it immediately into a cooling 

 vat, we simply keep the bacteria from multiplying. They remain dor- 

 mant, as it were, as long as the milk remains cold. But if the milk is 

 placed in a warm atmosphere, they will multiply as rapidly as though 

 they had never been chilled. To be successful, therefore, in handling 

 milk in the cold, it is necessary to cool it as soon as possible after 

 milking and to keep it cool until consumed. 



The heating of bacteria either checks their growth or kills them. 

 There is a great difference among the various species in regard to this. 

 While some are killed at 60° C, others seem to be uninfluenced and still 

 others merely have their growth checked. This is true at the different 

 temperatures ranging from 60° C. to 100° C. There is quite a number of 

 bacteria which will withstand a heating of 96° C. for twenty minutes 

 and will continue to grow as though they had not been subjected to any 

 enervating influence. The large class of lactic acid bacteria is mostly 

 destroyed at a temperature of 65° C. but there are a great many, usually 

 those containing spores, remaining that will cause various actions upon 

 milk. As a rule, they first curdle the milk, then peptonize it. 



It is not possible to heat milk indefinitely, without altering it 

 chemically, therefore destroying its palatability. In heating milk above 

 75° C. there is always produced a cooked taste. Consequently we are 

 limited in the application of heat as a means to exterminate bacteria. 



PASTEURIZATION AND STERILIZATION. 



This is simply the application of heat as the means to exterminate 

 some or all of the bacteria present in milk. Pasteurization consists in 

 heating the milk at 70° C. for twenty minutes (the temperature and time 

 are both variable). Pasteurization has been resorted to in order to 

 obviate the cooked taste in milk, to enhance its keeping qualities, to 

 kill disease-producing germs and to reduce the number of ordinary milk 

 bacteria. Its intrinsic value lies mainly in its destruction of disease-pro- 

 ducing germs. Concerning a further discussion of this matter, I take 

 pleasure in referring you to Bulletin 133, and the bulletin that follows. 



Complete sterilization is impracticable in the commercial handling of 

 milk. It produces a cooked taste in the milk rendering it unpalatable. 

 It changes the composition of milk, to a certain extent. There is no 

 demand for it. There are, however, purposes for which sterilization is 

 absolutely necessary, but for a commercial product, little can be said in 

 its favor. It is true that in sterilizing milk, we kill all the bacteria 

 present, yet this is no argument, inasmuch as ordinary milk bacteria 

 produce no direful effects in the animal economy. 



MILK FERMENTATIONS. 



Through fermentations in milk, bacteria manifest their presence. It 

 would make no especial difference how many bacteria entered the milk 



