442 CONTAMINATION AND DETERIORATION OF FOOD 



CANNING 



The alternative to control of a living flora in food is destruction of the micro- 

 organisms present by cooking or processing. 



The ordinary procedures used in preparing food for the table destroy the vegeta- 

 tive forms present, but leave the spores of many species of bacteria in viable condi- 

 tion. If such spores are abundant, the cooked food may and usually does spoil much 

 more quickly than the raw products since the tissues of the foodstuffs are usually bro- 

 ken down, or softened, hence more easily penetrable by organisms, and the water con- 

 tent is either actually increased or rendered more immediately available to bacteria 

 by the heating process. The bacteria surviving in good, sound food freshly and thor- 

 oughly cooked are not ordinarily a menace to the consumer who uses them at once. 

 Whatever danger there may be either from infection or from toxemia is dependent 

 upon storage with the incubation or reinfection of the cooked product. 



To prolong the holding period then, the product must either be sterilized or be 

 put under conditions where any surviving organism will fail to develop, as well as be 

 protected from contamination. Canning has been developed to cover these require- 

 ments. Although much canning has not reached true sterility, canning processes have, 

 as a rule, prescribed such methods of washing, precooking or blanching, exhausting 

 sealing, and cooking or processing in the can as reduces the free oxygen of the product 

 to a negligible minimum, destroys all vegetative forms present, and reduces or de- 

 stroys the bacterial spores which are nearly always present upon the raw foods. 



Extensive tests of canned foods have shown that spores of certain species of aero- 

 bic bacteria may be present in canned food without being able to grow there. Such 

 foods keep. Certain species produce highly resistant spores which survive the usual 

 cooking process, but which do not germinate at ordinary storage temperatures. If 

 the foods containing them (for example, canned corn) are quickly cooled and stored 

 under cool conditions, no spoilage results; but if the cans are allowed to cool 

 slowly over a considerable period, these "thermophiles" grow and spoil the food. 



The presence of these groups of highly resistant organisms in food has led to ex- 

 tensive studies of the thermal death-points of bacterial spores by the National Can- 

 ners' Association in their own laboratories and in Harvard University Medical School, 

 the University of California, and the University of Chicago. Such work brings us 

 step by step nearer to a safe food supply. 



The space of this article does not permit the discussion of the microbic floras of 

 food. Enough has been said to indicate the fundamental conditions encountered in 

 raw food and the principles of food handling which make possible the gathering and 

 marketing of these varied types of products with their burden of active or inactive 

 micro-organisms. A better knowledge of micro-organisms carried by food into the 

 household or the food factory may be expected to result in wider acceptance of an 

 ideal for the selection of foodstuffs: we should say, not, Is it bad enough to discard? 

 but, Is it right?' 



' For a more extensive discussion, cf. Thom, Charles, and Hunter, Albert C: Hygienic Funda- 

 mentals of Food Handling. Baltimore: Williams & Wilkins Co., 1924. 



