316 PRESERVATION METHODS 



fish (luring this holding period is of extreme importance to the ultimate 

 canned product quality. 



It is generally recognized that the canned product produced from fish 

 held for long periods, either iced or in refrigerated brine or sea water, 

 will be inferior in quality to that canned from absolutely fresh fish. De- 

 gradation (chemical, bacteriological, and/or autolytic) which occurs in 

 fishery products during this holding period may manifest itself in many 

 ways in the canned product — off odors and flavors, rancidity, forms of 

 product and container discoloration, poor texture, and, in extreme cases, 

 incipient spoilage. 



Changes at elevated or deck temperatures will be even more rapid than 

 those which take place under iced conditions. Ideally, therefore, fish 

 should be canned as soon as they are taken from the water. More practi- 

 cally, the time between catching and processing should be kept to an 

 absolute minimum. 



Fish Canning Procedures 



The actual canning procedures for individual fishery products are given 

 in the chapter covering the specific species of fish. We will consider here 

 only the differences in the canning procedures as related to the various 

 general classifications of fishery products. 



Standard Fish Packs. Fish may be divided into two broad categories 

 in relation to the amount of preparation necessary prior to filling: (1) 

 packed raw, i.e., no precook, and (2) those species which require a pre- 

 cook of some sort prior to filling. 



No Precook. Under this classification the whole fish is washed, 

 butchered, cut to can height pieces either mechanically or by hand, 

 filled with added salt, closed, and processed. Fish canned by this simplest 

 of methods include salmon, mackerel, shad, and alewife or river herring. 



Precooked. The best example of this class of fish is tuna, which is 

 eviscerated, then precooked prior to butchering, cleaning, cutting, and 

 filling. The precook, which will vary from 2 to 12 hours at 216 to 220°F, 

 depending on the size and species of tuna, is one of the most important 

 parts of the tuna operation. Its purpose is threefold: first, to remove or 

 cook-out a portion of the natural oil; second, to loosen the meat on the 

 bones so that subsequent cleaning operations may be carried out more 

 efficiently; and, third, to obtain proper texture in the final canned product. 



Other fish in this class are sardines, herring, anchovies, and related 

 species and are categorized by a high oil content which must be mini- 

 mized prior to canning. With the exception of tuna, the pre-cook may be 

 accomplished after the fish is tilled into the can by a short steam exhaust 

 followed by inversion to drain. 



