156 Microbes and You 



count and expect to make a good product out of it by merely freez- 

 ing the material, any more than you can make high quality pasteur- 

 ized milk from poor raw material simply by heating the milk to 

 destroy the bacteria. It just doesn't work. With the recent popu- 

 larity of home freezers, the notion that freezing kills microbes is a 

 concept that needs to be dispelled. It must be conceded that 

 freezing may lower the bacterial count, because the "weaker" or- 

 ganisms will not tolerate such a minimal metabolism, if life proc- 

 esses do go on at these low temperatures. An interesting ob- 

 servation along this line, however, is that pork containing living 

 trichina worms can be made "safe" by freezing for 24 hours. Please 

 don't confuse trichina worms with bacteria. 



The substrate in which organisms are frozen has a great deal 

 to do with the lethal effects of the temperature. While the typhoid 

 organism normally cannot survive freezing in water for more than 

 six months, this same organism has been found to be still viable 

 after two years at — 4° C. in frozen ice cream. When an organism 

 cannot grow, it oftentimes will die, but the length of survival de- 

 pends upon a number of environmental factors. One suggested 

 explanation of death of microbes in the frozen state is suffocation 

 brought on by too much oxygen, since the oxygen concentration at 

 0° C. is twice that found at 30° C. in many substrates. The re- 

 distribution of materials by freezing is another interesting reaction. 

 A 10% sugar solution when frozen may be found to have as low as 

 2% sugar around the edge which is frozen first, while the core may 

 have as high as a 35% concentration of the sugar. Perhaps a similar 

 redistribution of protoplasm within the cell occurs, and if the 

 condition is not relieved in time, the cell perishes. Cold, in 

 general, should be considered as a bacteriostat, not as a germicide. 

 It has been shown that bacteria grow at —8.89° C. (16° F. ), and 

 while metabolism may be at an extremelv low rate, life processes, 

 nevertheless, have been reported. When materials are frozen the 

 moisture is not available, or at least it is not as readily available, 

 and this might be compared to drying a culture. Since water 

 usually is considered to function as a carrving agent for food and 



