HEAT IN THE PRESERVATION OF FOOD PRODUCTS. 385 



ration of agreeableness to the taste is, however, more seeming than real, 

 and arises largely from prejudice of the consumer against food conserved 

 in tin cans, rather than from any actual change. When the preserving 

 is properly done, the product should be no less attractive to the eye, no 

 less pleasing to the palate, and of no less value from the standpoint of 

 digestibility than the same food when served in the fresh condition. 



BIOLOGICAL CHANGES. Vital Disorganization. The entire industry 

 of conservation of foods by means of heat is based on a microbiological 

 process. It is a universally recognized fact that the ordinary spoilage of 

 food is a microbiological change, hence the individual desirous of 

 protecting food from spoilage must give consideration to the microbial 

 agents responsible for the change. 



Normal Flora and Fauna. Aside from a few types of organisms 

 causing disease or specific poisonous conditions, we are unable to desig- 

 nate definite species as those causing canned goods to spoil. Considering 

 the great variety of foods preserved by heat, and the different conditions 

 under which they are grown and secured, it naturally follows that the 

 normal flora and fauna of food to be preserved in this manner would 

 embrace a wide variety of species, including molds, and spores of higher 

 fungi, yeasts, bacteria, and animal parasites. Generally speaking, the 

 microbial flora of fruits consists mostly of molds and yeasts, although 

 bacterial forms may also be present. In the case of vegetables, and of 

 fruits coming in contact with the earth, more species of bacteria are apt 

 to be present, many of them spore formers able to withstand a high tem- 

 perature. Finally, in meats and fish the living forms may include not 

 only molds, yeasts, and bacteria, but animal forms as well, such as the 

 organisms of taeniasis (tapeworm) and trichinosis. In the preserving 

 industry, therefore, consideration must be given to all these forms, not 

 only from the standpoint of the successful preservation of the various 

 foods, but also from that of protecting the health of the consumer from 

 possible poisonous substances present or produced in the conserved food, 

 and from possible infection with pathogenic organisms present in the food 

 before it is packed. 



PASTEURIZATION. 



ECONOMIC CONSIDERATIONS. In the preservation of food by heat, 

 two processes are applicable, pasteurization and sterilization. In pasteur- 

 ization, the aim is not to effect the permanent preservation of foods or 

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