LOW TEMPERATURES 177 



ing from 45 to 50 F., it is evident that bacterial growth 

 is greatly retarded by maintenance of food material under 

 readily available low-temperature conditions. 



The zone of bacterial existence is far wider than the 

 zone of growth. This fact is of importance in the storage 

 of foods, for when they are removed from storage, the 

 microorganisms lliat were present when the foods went into 

 storage begin to grow, and the decomposition changes rap- 

 idly occur. Indeed, with some foods, especially meats, 

 these changes develop after freezing with even increased 

 rapidity, owing to the fact that the muscle fibers are forced 

 apart by the freezing process, allowing the cell juices to 

 exude from the cells themselves. This permits the bacteria 

 to act more readily on the meat than when confined ex- 

 clusively to the surface. Even after storage at extremely 

 low temperatures, below F., foods spoil rapidly; for 

 while alternate freezing and thawing are very injurious to 

 bacterial life, microorganisms are able to withstand expos- 

 ure to low temperatures for prolonged periods of time. 



In the storage of foods at low temperatures, the effect 

 of freezing on the physical properties of food must be 

 considered. For example, eggs, fruits, and vegetables can 

 not be stored without injury at temperatures at which 

 freezing will occur. If milk is frozen and allowed to re- 

 main in this condition for any considerable period, the fat 

 is altered physically, so that on thawing it does not mix 

 thoroughly with the serum. Longer exposure causes the 

 casein to separate. 



In the case of foods that can be stored with impunity at 

 temperatures below freezing, the period of storage may be 

 greatly extended; but with such foods as milk and eggs, 

 where storage must be above freezing, the holding period 

 is limited because of the fact that bacterial development 

 can occur at temperatures slightly above freezing. In 



