56 BACTERIA, YEASTS, AND MOLDS 



microorganisms but merely has to seal it in such a way as 

 to keep out air and thus to prevent mold growth. 



Temperature. Molds, like bacteria and yeasts, require a 

 moderately warm temperature for vigorous growth. At a 

 temperature slightly below freezing they will not grow at 

 all, and at a few degrees above freezing their growth is very 

 slight. Some species of molds, however, grow readily 

 enough at 40°, growing better at this than at a warmer 

 temperature. Hence it follows that the temperature of 

 an ice chest will not wholly prevent molding. The still 

 lower temperatures of mechanical refrigerators are more 

 efficient, while those of cold storage (slightly below freez- 

 ing) prevent mold growth almost entirely. Most common 

 molds, however, either fail to grow at an ice-chest tempera- 

 ture or grow very slowly. As the temperature increases, 

 however, the growth becomes more vigorous, and at tem- 

 peratures varying from 70° to 100° the growth of these 

 plants is stimulated to their highest activity. A practical 

 result from these facts is that any material which can be 

 kept sufi&ciently cool will fail to show signs of mold, even 

 though tightly closed in an atmosphere saturated with 

 moisture and abundantly sown with mold spores. 



Killing by Heat. In considering the relation of tem- 

 perature to molds a fact of great importance is that high 

 heat will always destroy molds and their spores. Boiling or- 

 dinarily kills spores as well as mycelium. Hence any food 

 which has begun to mold, and which is of a character to 

 allow heating, may be protected from the further growth 

 of the mold by boiling. This method of treatment will be 

 possible for many preserves, canned foods, or any food that 

 has been previously cooked. It may be applied to preserves. 



