CHAPTER 8A Heat Processing of Shellfish EIICHI TANIKAWA Laboratory of Marine Food Technology, Faculty of Fisheries, Hokkaido University, Hakodate, Japan AND SHAMSUD DOHA1 Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan I. Introduction 305 II. Crustacean Shellfish 306 A. Crabs 306 B. Lobsters 318 C. Shrimps and Prawns 321 III. Molluscan Shellfish 324 A. Oysters 324 B. Scallops 326 C. Abalones 327 D. Clams 328 E. Sea Mussels 331 F. Other Molluscs 333 References 334 I. Introduction Shellfish include crustaceans and molluscs and sometimes other marine invertebrates. As individual categories are not always separated in production statistics, their relative importance is difficult to ascertain. However, a commonly accepted figure is that crustaceans comprise 2% of the total fish catch and molluscs 6%. For crustaceans, the leading producers are the United States, Japan, India, Mexico, and the U.S.S.R. with 5-year averages of 196,300; 120,300; 104,200; 51,000; and 33,700 metric tons production, respectively. Most of these are consumed fresh or frozen. Probably the oldest method of preserving shellfish is by drying. This is still practiced in a few countries. With the advent of canning, this gradually replaced drying. However, canning has in turn become super­ seded by freezing in many areas. The notable exception is in the U.S.S.R., 1 Present Address: Department of Fisheries, East Pakistan Agricultural University, Mymensingh, East Pakistan. 305 306 EIICHI TANIKAWA AND SHAMSUD DOHA where the major portion of the crustacean catch is the Pacific king crab. Most of these are processed at sea. Canned Russian crabmeat has under the trade name of "Chatka" become almost a gourmet article, equivalent to caviar. It is sold in a number of countries around the globe. (Squid processing is discussed in Chapter 8B.) II. Crustacean Shellfish A. CRABS The following crab species are economically important and heat processed in cans: The United States: blue crab (Callinectes sapidus); Dungeness crab (Cancer magister); king crab (Paralithodes camtschatica); rock crab (Cancer irroratus). Canada: Dungeness crab (Cancer magister). Japan: abura-gani (Paralithodes platypus); hanasaki-gani (P. brev- ipes); ke-gani (hair crab, Erimaerus isenbeckii); taraba-gani (king crab, P. camtschatica); zuai-gani (Chionoecetes opilio). Blue crab. The blue crab is common along the U.S. coast from Mas­ sachusetts to Texas. Although it accounts for 67% of the production of crab meat in the U.S. (Power, 1962), it is marketed almost entirely as fresh meat. The canning of this species is not a very sizable industry; it is much smaller than that of either the Dungeness or king crab. The cost per pound of picking the meat is greater and it is within easy reach of the principal centers of consumption. Dungeness crab. The Dungeness crab is common on the Pacific coast of North America and is found from Lower California to Alaska. Canning is done in Oregon, Washington, British Columbia (Canada), and Alaska. Some specimens measure 10 inches across the back shell. In size, it is next to giant crabs of Alaska and the Bering Sea. It lives from the low tide mark to about 50 fathoms, but is not often fished in the waters around British Columbia below 20 fathoms (Dewberry, 1959a). Rock crab. The rock crab is most common on the New England coast, but its canning is not economically important. Alaska king crab and related species. The Alaska king crab belongs to the genus Paralithodes and comprises three species: P. camtschatica, P. brevipes, and P. platypus. Paralithodes camtschatica is found in Alaskan waters and the Bering Sea (Dassow, 1950). It is processed by American, Soviet, and Japanese canners. The last have 5000-6000-ton vessels on which complete canneries are installed, operating in Alaskan waters and the Bering Sea. The U.S. fishery for this species is minor. Alaska king crab is the largest crab, averaging about 12 lb. (5.5 kg.) in weight and measuring 3.5-4 ft. from leg tip to leg tip. The carapace 8A. HEAT PROCESSING OF SHELLFISH 307 is small in comparison to the legs, measuring 7-9 inches across, and covered with spines. These spines are used for species identification. It is estimated that the meat from one leg is equivalent to the contents of two 1-lb. cans of crab meat. Paralithodes brevipes and P. platypus are not found in Alaskan waters, but in the Bering Sea. These crabs are not plentiful. Zuai-gani (Chionoecetes opilio), a related species, is found on the Japan Sea coasts of the main islands of Japan and off Korea. It is good in flavor but not very abundant. Hair crab. Canning of the horse hair crab (ke-gani, Erimacrus isenbeckii) is next in importance to Alaska king crab in Japan. Hair crab is found along the northern coasts of Hokkaido, Japan, off the western coast of Sakhalin, and in waters around the Kuril Islands. It is also found in Alaskan waters. 1. Canning Crabs Procedures in the canning depend on the species. They will be treated separately. a. UNITED STATES (i) Blue crab. The blue crab was first canned in the U.S. in 1878 (Jarvis, 1943). Canning its meat by conventional methods has resulted in a product of inferior flavor and color. By dipping the crab meat in brine solution containing lactic acid the method was improved (Fellers, 1936). The strength of the lactic acid is just sufficient to insure an acid pH of the meat. Small amounts of aluminum or zinc sulfate, not exceed­ ing 0.04%, are added to this brine dip. The crabs are selected according to season, sex, locality, and time of moulting. Lightly cooked crab meat is packed in parchment-lined 6.5-oz. flat cans, sealed under high vacuum, and processed at 250°F. for 30 min. It is advocated that the flake or lump meat be canned separately from the meat removed from the claws (Tressler and Lemon, 1951). (it) Dungeness crab. The dorsal shell or carapace is removed by fastening the edge of the shell over a stationary hook and giving a sharp jerk. Then each crab is cut in half by a large stationary knife. The viscera are removed and the body is thoroughly washed and taken to large tanks of heated fresh water. In some canneries sodium bicarbonate is τ added in the ratio of /2 lb. to 40 gallons of water, but this practice is not recommended. The crabs are dumped into tanks of boiling water and cooked for about 20 min. Some packers precook the crabs in a steam chest for about the same length of time at a temperature of 212-220°F. (100-104°C). More of 308 EIICHI TANIKAWA AND SHAMSUD DOHA the flavor of the meat is believed to be retained by this process, but packers who use the boiling-water method maintain the meat is more readily picked from the shells. The shell on the legs is cracked with a small wooden mallet and pounded. This loosens and releases the meat without breaking it into small flakes. Body meat and leg meat are kept separate. About equal proportions of each are obtained. The picked meat is dipped in dilute acetic acid, 2 oz. 28% acetic acid to 1 gallon of water, for about 1 min. It is then washed in fresh water, dipped in 100° salinometer brine, pressed to remove excess moisture, drained, and taken to the filling tables. Dungeness crab is packed in cans of three sizes: "half flats," "pound flats," and "No. 2" cans, with net weights of 6.5, 13, and 17 oz. (184.3 g., 368.6 g., and 482.0 g.), respectively. All cans are lined with sea-food formula C-enamel, and a lining of vegetable parchment paper is inserted as an added protection before filling. Hand packers fill the cans with body meat. About oz. salt is added to each can. The trays of filled cans are sealed in a vacuum closing machine. The sealed cans are packed in salmon coolers and processed. There is some variation in processing, but all packers agree that it must be closely controlled. Ten-pound steam pressure has an adverse effect on the color of the crab meat. Representa­ tive processes now in use are: half flats, 90 min. at 221°F. (105°C.) (3-lb. pressure); 1-lb. flats and No. 2 cans, 80 min. at 228°F. (108.9°C.) (5-lb. pressure). The cans, upon removal from the retort, are cooled by a water spray system and cleaned; they are labeled and packed in wooden or fiberboard cases holding 96 half flats, 48 1-lb. flats, 24 No. 2 cans (Jarvis, 1943). (in) Alaska king crab: Preparation. The first operation in the butch­ ering of this crab is removal of the carapace. This is done by hooking the shell over the sharp edge of the butchering tool. The ventral shell is then broken along the midline, leaving the legs attached to each portion. The gills, viscera, etc. are then removed by washing and trim­ ming. The cleaned carcasses are immediately placed in a vat of boiling water for 15-17 min. The boiling water may be either fresh water or 3% brine solution. After cooking, they are cooled in cold running water for about 30 seconds. The meat separates from the shell during cooking. The legs are cut into segments the height of the can. The meat is shaken out of the shell into a pan, leaving the tendons attached to the shell. The leg and body meats are kept separate until packed in the cans. When the pans are filled, the meat is dumped into a stainless steel wire basket and washed with a cold water spray to remove any particles of shell.