314 PRESERVATION METHODS 



measuring the time necessary for the heat to penetrate to the slowest 

 heating portion. In order to simplify this subject, let us say that once the 

 thermal death time or the lethality necessary to destroy spoilage bacteria 

 is known and the rate of heat penetration determined, a sufficient process 

 may be calculated for the canned food in question. 



With ''acid" foods, processing may be accompHshed in boiling water; 

 however, for ''low acid" foods the time necessary to accomplish sterility 

 at the relatively low temperature of boiling water would be extremely long. 

 Hence, for "low acid" foods, it is necessary to process under superimposed 

 steam pressure at temperatures substantially above 212°F to accomplish 

 the required lethality in a practical length of time. Since the length of 

 process decreases with increasing temperature, the limitation of the tem- 

 perature of processing then becomes dependent upon two factors : equip- 

 ment and the effect of temperature on product quality. 



For fishery products, normally having a pH range of 6.0 to 7.5, 240 to 

 250°F processes are most commonly used, the length of time being de- 

 pendent upon the size of the container in which the food is packed and 

 the type of pack. Suggested processes may be found in NCA Bulletin 26L^ 



Correct processing is nothing to be taken lightly and recommended 

 processes should not be modified without careful determination of the 

 modification's effect on sterility. Research organizations, such as the 

 National Canners' Association, the major can and glass companies, and 

 processing equipment manufacturers may be consulted for detailed infor- 

 mation on processing. 



Other methods of processing such as aseptic canning — in which a pre- 

 sterilized product is filled into a sterilized container and sealed under 

 aseptic or sterile conditions — are a commercial reality for certain prod- 

 ucts, primarily liquids. Methods such as radiation sterilization are still in 

 the experimental stages. While many new methods of processing are being 

 investigated, the basic method remains that of retorting or processing 

 under superimposed steam pressure either in batch or in continuous 

 cookers. 



Production of Canned Fishery Products 



In 1959, the world catch of fishery products amounted to almost 78 

 billion pounds^ The United States catch of fishery products in that year, 

 6.4 billion pounds, may be broken down as follows: fresh market — 43 per 

 cent, cured — 20 per cent, reduction to meal and oil — 17 per cent, canned — 

 9 per cent, freezing — 8 per cent, and miscellaneous — 3 per cent. 



In the United States there were over 360 plants canning fishery prod- 

 ucts in 1960, and although some 100 various fishery products were canned, 

 the following were the most common (listed in the order of total value of 



