METHODS OF FOOD PRESERVATION. 1023 



ually raise the heat to a temperature between 70 and 77, keeping it 

 there for half an hour. The caution was given not to heat higher or 

 longer, as the fruit would be liable to burst. Lastly, the bottles were 

 to be filled with boiling water to within an inch of the neck, corked 

 immediately and laid upon their sides in order that the hot water might 

 swell the corks, After covering the corks with cement, the operation 

 was complete. 



The credit for the discovery of this process, however, is generally 

 given to M, Appert, who was the first to put it into use on the large 

 scale. In 1810 M. Appert published a book giving directions for this 

 method of food preservation, for which he was awarded the prize of 

 12,000 francs offered in 1809 by the French Government for a process of 

 preserving perishable alimentary substances. Appert's directions were 

 to partially cook the food and put it into strong glass bottles, filling 

 them almost to the top. These bottles were then to be securely corked 

 and exposed for some time to the action of boiling water. To guard 

 against accident, each was to be separately covered with a cloth bag, 

 and the water in which they were plunged was to be gradually heated, 

 starting -cold. The boiling temperature was maintained for an hour, 

 and then the fire was drawn and the bath and bottles allowed to cool 

 slowly. Peas and beans were to be put in the bottles in the raw state, 

 and the boiling temperature maintained for about two hours. 



This method is, of course, founded on the same principle as the bac- 

 teriological operation of sterilizing. None of the common bacteria can 

 survive the action of boiling water for more than a few minutes, and, 

 although their spores are more resistent, even these will not usually 

 survive more than half an hour. Moreover, few of the common putre- 

 factive bacteria are spore-producing. The bactericidal action of heat 

 in the canning process is much facilitated by the fact that in most cases 

 the liquids surrounding the canned foods are weakly acid. Bacteria 

 are much more susceptible to heat in an acid liquid than in one which 

 is neutral or alkaline. 1 



For many years the fact of the preservation of foods treated by this 

 process was ascribed solely to the fact that all air is expelled from the 

 can during the process of canning, it being supposed that air was abso- 

 lutely necessary for the putrefactive process, or at least was necessary 

 to initiate it. This is, of course, not so. Some of the common bacteria 

 causing putrefaction are absolutely anaerobic, and the presence of air 

 is fatal or detrimental to them, so that they flourish in the interior of 

 decaying masses, but are not found on the surface; to others, air is not 

 necessary though not detrimental, while many again flourish only when 

 it is present. It follows that the mere presence or absence of air in the 

 interior of the can is a matter of no importance in itself. Tyndall dem- 

 onstrated the fact that air played no important part in putrefaction, 2 



1 Tyndall: Floating Matter of the Air (New York: 1882), 203. 



2 lUd, 85 and 88, 



