THE SHRIMP FISHERY 175 



In the Pacific Northwest and Alaska the shrimp canning process differs 

 from that described for the Gulf of Mexico and South Atlantic areas as 

 a consequence of the different kind of shrimp involved and different 

 canning concepts. The following information is reproduced through the 

 courtesy of L. W. Strasburger of New Orleans: Some plants in Alaska 

 and the Pacific Northwest ''age" their shrimp by holding them in ice 

 or refrigerated seawater for two to four days. This is said to aid in the 

 peeling operation. Blanching times are from 45 seconds to 1}^ minutes. 

 Citric acid is added to the brine placed in the can. The brine is added 

 cold. Vacuum closing machines are used in this industry, instead of 

 depending on hot brine to produce a vacuum. Processing times vary 

 from 18 to 24 minutes at 240°F. 



In common with several other canned fishery products, canned shrimp 

 sometimes contain crystals of water-insoluble magnesium ammonium 

 phosphate hexahydrate, ordinarily called struvite. These crystals resemble 

 glass fragments and they sometimes produce unfavorable consumer reac- 

 tion, even though they are harmless. Magnesium is the limiting factor 

 in the formation of struvite crystals, and one method of control is to 

 leach the product in order to remove magnesium. A more successful 

 method is to keep the crystal from forming by adding a sequestering 

 agent. A method patented by the Blue Channel Corporation of Port 

 Royal, South Carolina involves a mixture of aluminum sulfate and EDTA 

 (Calcium disodium ethylene diamine tetraacetate), known as Strucol. 

 This is added to the can of shrimp in the form of tablets or dissolved 

 in the brine (Strasburger, personal communication). 



Shrimp canners also encounter problems of discoloration of the inside 

 of cans and of the shrimp meats resulting from the formation of iron 

 sulfide. This seems to be associated with a high pH of the shrimp meat. 

 White shrimp and most of the other common varieties have a normal 

 pH of about 6.8; values of 7.2 and above allow increased discoloration^^ 

 Lowering the pH by the addition of citric acid or lemon juice reduces the 

 discoloration but sometimes impairs the flavor and texture of the finished 

 product. The discoloration is especially prevalent with sea bobs and is 

 one reason that this species has not been more used for canning. 



Freezing. Frozen Shell-on Shrimp. About 40 per cent of the shrimp 

 produced in the United States is frozen raw with the shell on but the 

 head removed. These shrimp are usually sold in five-pound packages. 

 Commonly, bulk purchases of ''fresh" shrimp at meat counters in retail 

 stores are in reality frozen raw shrimp which have been thawed and 

 placed on the counter as needed. Frozen shrimp in this form are sold 

 to wholesalers, retailers, to the restaurant and hotel trade, and to proc- 

 essors of breaded shrimp. 



