CANNED FISHERY PRODUCTS 317 



Shellfish. The canning of shellfish differs from that of fish in that all 

 shellfish are precooked to some extent prior to filling and, in addition, 

 usually require further treatment such as brining, acidification, blanch- 

 ing, or a combination of these. Clams and oysters are steamed to open 

 the shell, firm the meat slightly, and ease removal. 



Crabs, which must be alive when the canning procedure begins, are 

 butchered by removing the carapace or back shell, eviscerated, washed 

 thoroughly, and then precooked 10 to 15 minutes in boiling water or 

 steam prior to picking. In addition, crab meat is usually dipped and/or 

 packed in a citric acid brine to prevent product discoloration. Shrimp, 

 which after being peeled are blanched for 5 to 7 minutes in a boiling brine 

 prior to packing, are also packed in brine. This brine may also contain 

 citric acid if product discoloration is a problem. 



Another difference between the canning of fish and shellfish is the 

 packing media ; fish usually are packed dry or with oil while shellfish are 

 normally packed with added brine. 



Specialty Products. Specialty products may be defined as high-priced, 

 limited volume items which usually require more than the normal amount 

 of preparation. 



Specialty fishery products canned in the United States in 1960 are 

 tabulated in Table 24.2. 



A specialty product usually requires additional preparation and treat- 

 ment such as brining, smoking, grinding, addition of ingredients other 

 than fish, and special packing and processing techniques. The procedure 

 for canning a specific item is usually developed by the packer and the 

 details of the method are not usually publicized. 



Canning Equipment 



Since the basic butchering, cleaning, cutting, and filling equipment 

 used today is discussed under the chapter relating to the specific spe- 

 cies, we will discuss here only closing equipment, methods of obtaining 

 vacuum, and retorts. Related canning equipment such as track work, 

 unscramblers, labelers, and casing equipment, which is many instances 

 are designed for a specific plant operation, will not be discussed. 



Can Closing Equipment. Closing equipment or double seaming equip- 

 ment may vary tremendously in appearance, size, design, number of 

 seaming heads, and speed, depending on the manufacturer and the spe- 

 cific canning operation for which such equipment is intended. Seamers 

 may vary from a hand-operated, laboratory style to a simple single sta- 

 tion machine operating at speeds of 30 to 60 cans per minute or to multi- 

 ple station, oil-driven equipment, operating at can closing speeds of over 

 1000 cans per minute. In all cases, however, the basic purpose is to her- 



