HEAT 185 



secured by heating the product to the boiling-point on three 

 successive days, as described on page 36. Small steam- 

 pressure cookers have also been recently introduced for 

 household use. In the canning of fruits in the home, the 

 sugar that is added for flavor aids in the preserving process, 

 through the fact that it increases the concentration of the 

 liquid and also raises the boiling-point of the solution so 

 that the spores are subjected to a temperature above 

 212 F. 



It has been shown by recent investigation that much- of 

 the canned material is not sterile. It is not essential that 

 any material be free from all living microorganisms or 

 their spores in order to be protected from decomposition. 

 If the organisms present are unable to grow under the con- 

 ditions that obtain in the material, their presence is of no 

 importance. The spores of many aerobic bacteria are 

 amonir the most resistant, and are most likely to persist 

 in foods after processing. In the sealed can that has been 

 largely freed from air before being sealed, the aerobic 

 spores can not germinate. The spores of anaerobic bac- 

 teria in the food are far more likely to cause trouble in 

 canned goods than those of aerobic forms. The develop- 

 ment of the spores of anaerobic forms may be prevented by 

 concentration, acids, and preservatives. 



