STERILIZATION FOR CANNING 171 



forms of life, and hence the simple heating of food will 

 destroy all bacteria. The material to be canned must be 

 cut up into pieces of convenient size, which will depend 

 somewhat upon the kind of material. In general, the 

 larger the pieces, the more attractive the appearance of 

 the product when finished but the greater the difficulty 

 of canning. Cherries, plums, and berries can be left 

 whole. Pears are cut into halves or quarters, while apples 

 are commonly cut into smaller pieces. These pieces are 

 to be placed in water and the whole brought to a brisk 

 boil, — this temperature being chosen because it is easily 

 obtained and because it is sufficient in most cases to destroy 

 the bacterial life. The process of canning is, therefore, 

 applicable only to materials that are not greatly injured by 

 immersion in water and subsequent boiling. Hence it is 

 useful for foods which cannot be well preserved by drying. 

 In the application of heat several points must be borne 

 in mind. i. It must be remembered that the destruc- 

 tion of the bacteria must be absolute. If a single indi- 

 vidual bacterium is left alive in the food after the boiling, 

 the whole process is useless, and the canning will be a 

 total failure. One live bacterium will be capable of grow- 

 ing and multiplying, producing a subsequent putrefaction 

 and destruction of food with just as great certainty, though 

 not so quickly, as if a million of them were left alive. The 

 preliminary heating must therefore be a complete sterili- 

 zation, that is, a heating so thorough that every individual 

 bacterium is destroyed. No half-way processes are of any 

 use whatsoever ; it must be total and absolute. This is 

 by no means easy, and most failures in canning are due 

 to the inability to bring about this complete destruction. 



