Heat Processing of Shellfish
EIICHI T A N I K A W A
Laboratory of Marine Food Technology, Faculty of Fisheries, Hokkaido University, Hakodate, Japan
A N D
S H A M S U D D O H A1
Department of Fisheries a n d 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 a c c e p t e d figure is that crustaceans comprise 2 % of the total fish c a t c h and molluscs 6 % .
F o r crustaceans, the leading producers are the U n i t e d States, J a p a n , India, Mexico, and the U.S.S.R. with 5-year averages of 196,300; 120,300;
104,200; 51,000; and 33,700 m e t r i c tons production, respectively. Most of these are consumed fresh or frozen.
P r o b a b l y the oldest m e t h o d of preserving shellfish is b y drying. T h i s is still p r a c t i c e d in a few countries. W i t h the advent of canning, this gradually r e p l a c e d drying. However, canning has in turn b e c o m e super
seded b y freezing in m a n y areas. T h e 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
is small in comparison to t h e legs, measuring 7 - 9 inches across, and covered with spines. T h e s e spines are used for species identification.
I t is estimated that the m e a t from one leg is equivalent to t h e contents of two 1-lb. cans of c r a b meat.
Paralithodes brevipes and P. platypus are not found in Alaskan waters, b u t in the B e r i n g Sea. T h e s e crabs are not plentiful.
Zuai-gani (Chionoecetes opilio), a related species, is found on t h e J a p a n S e a coasts of the main islands of J a p a n and off K o r e a . I t is good in flavor b u t not very abundant.
Hair crab. C a n n i n g of the horse hair c r a b (ke-gani, Erimacrus isenbeckii) is next in importance to Alaska king c r a b in J a p a n . H a i r crab is found along the northern coasts of Hokkaido, J a p a n , off the western coast of Sakhalin, and in waters around the Kuril Islands. I t is also found in Alaskan waters.
1. Canning Crabs
Procedures in the canning depend on the species. T h e y will b e treated separately.
a. UNITED STATES
(i) Blue crab. T h e blue c r a b was first c a n n e d in the U . S . in 1 8 7 8 (Jarvis, 1 9 4 3 ) . Canning its m e a t b y conventional methods has resulted in a product of inferior flavor and color. B y dipping the c r a b m e a t in brine solution containing lactic acid the m e t h o d was improved ( F e l l e r s , 1 9 3 6 ) . T h e strength of the lactic acid is just sufficient to insure an acid p H of the meat. Small amounts of aluminum or zinc sulfate, not exceed
ing 0 . 0 4 % , are added to this brine dip.
T h e crabs are selected according to season, sex, locality, and time of moulting. L i g h t l y cooked c r a b m e a t is p a c k e d in parchment-lined 6.5-oz.
flat cans, sealed under high vacuum, and processed at 2 5 0 ° F . for 3 0 min.
It is advocated that the flake or lump m e a t b e c a n n e d separately from the m e a t removed from the claws ( T r e s s l e r and L e m o n , 1 9 5 1 ) .
(it) Dungeness crab. T h e dorsal shell or c a r a p a c e is removed b y fastening the edge of the shell over a stationary hook and giving a sharp jerk. T h e n e a c h c r a b is cut in half b y a large stationary knife. T h e viscera are removed and the b o d y is thoroughly washed and taken to large tanks of h e a t e d fresh water. I n some canneries sodium b i c a r b o n a t e is added in the ratio of τ/2 lb. to 4 0 gallons of water, b u t this p r a c t i c e is not r e c o m m e n d e d . T h e crabs are d u m p e d into tanks of boiling water and cooked for about 2 0 min.
S o m e packers precook the crabs in a steam chest for about the same length of time at a temperature of 2 1 2 - 2 2 0 ° F . ( 1 0 0 - 1 0 4 ° C ) . M o r e of
3 0 8 EIICHI TANIKAWA AND SHAMSUD DOHA
the flavor of the m e a t is believed to b e retained b y this process, b u t packers who use the boiling-water m e t h o d maintain the m e a t is m o r e readily p i c k e d from the shells. T h e shell on the legs is cracked with a small wooden mallet and pounded. This loosens and releases the m e a t without breaking it into small flakes. B o d y m e a t and leg m e a t are kept separate. About equal proportions of each are obtained.
T h e picked m e a t is dipped in dilute acetic acid, 2 oz. 2 8 % acetic acid to 1 gallon of water, for about 1 min. I t is then w a s h e d in fresh water, dipped in 1 0 0 ° salinometer brine, pressed to remove excess moisture, drained, and taken to the filling tables.
Dungeness crab is p a c k e d in cans of three sizes: "half flats," "pound flats," and "No. 2 " cans, with net weights of 6.5, 13, and 17 oz. ( 1 8 4 . 3 g., 368.6 g., and 482.0 g . ) , respectively. All cans are lined with sea-food formula C-enamel, and a lining of v e g e t a b l e p a r c h m e n t paper is inserted as an added protection before filling. H a n d packers fill the cans with body meat. About oz. salt is added to e a c h can. T h e trays of filled cans are sealed in a vacuum closing machine. T h e sealed cans are p a c k e d in salmon coolers and processed. T h e r e is some variation in processing, b u t all packers agree that it must b e 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, 9 0 min. at 2 2 1 ° F . ( 1 0 5 ° C . ) (3-lb.
p r e s s u r e ) ; 1-lb. flats and No. 2 cans, 8 0 min. at 2 2 8 ° F . ( 1 0 8 . 9 ° C . ) ( 5 - l b . pressure). T h e cans, upon removal from the retort, are cooled b y a water spray system and cleaned; they are labeled and p a c k e d in wooden or fiberboard cases holding 9 6 half flats, 4 8 1-lb. flats, 2 4 No. 2 cans (Jarvis, 1 9 4 3 ) .
(in) Alaska king crab: Preparation. T h e first operation in the butch
ering of this crab is removal of the carapace. This is done b y hooking the shell over the sharp edge of the butchering tool. T h e ventral shell is then broken along the midline, leaving the legs attached to each portion. T h e gills, viscera, etc. are then removed b y washing and trim
ming.
T h e cleaned carcasses are immediately placed in a vat of boiling water for 1 5 - 1 7 min. T h e boiling water m a y b e either fresh water or 3 % brine solution. After cooking, they are cooled in cold running water for about 3 0 seconds.
T h e m e a t separates from the shell during cooking. T h e legs are cut into segments the height of the can. T h e m e a t is shaken out of the shell into a pan, leaving the tendons attached to the shell. T h e leg and body meats are kept separate until p a c k e d in the cans. W h e n the pans are filled, the m e a t is dumped into a stainless steel wire basket and washed with a cold water spray to r e m o v e any particles of shell.
T h e washed m e a t is weighed and then dipped into w e a k acid solu
tion for 1 5 seconds. A c e t i c acid is generally used in preparing the acid dip although some packers prefer citric acid.
T h e acid dip is prepared b y adding 2 oz. glacial a c e t i c acid to e a c h gallon of fresh water, a solution p H 3.0. I f citric acid is used it is of about the same proportion and p H . T h e strength of the acid dip is maintained b y addition of fresh acid after e a c h 1 0 0 lb. crab m e a t is treated. T h e leg and claw m e a t is immersed in a 9 0 ° salinometer brine bath for about 1 5 seconds. T h e "white" or body m e a t is seldom given the brine dip as the leg m e a t absorbs sufficient salt to flavor the canned product.
(iv) Alaska king crab: Processing. K i n g c r a b m e a t is generally p a c k e d in y2-\b. flat tin cans lined with p a r c h m e n t and sea-food formula C - e n a m e l . Occasionally a p a c k e r will use J ^ - a n (i l - l b . c a ns f °r special markets. L a r g e pieces of leg and claw m e a t and broken pieces of the leg and claw are p l a c e d in the center. T h e tops are vacuum-sealed on the cans. T h e y are p l a c e d in a retort for processing for 7 5 min. at 6 l b . pressure and 2 3 0 ° F . ( 1 1 0 ° C ) . T h e cans are cooled in a spray of cold water as soon as they are removed from the retort ( T r e s s l e r and L e m o n , 1 9 5 1 ) .
b . CANADA
History records that the Dungeness crab was canned commercially for the first time in British C o l u m b i a in 1917.
(i) Preparation. T h e live crab is killed b y removing the carapace.
T h e b o d y is then either broken or cut in half. After the gills and offal are removed, the halves are thoroughly washed under a j e t of clean water. T h e y are placed in stainless steel wire baskets and lowered into brine tanks kept boiling b y live steam and cooked for 10 min. T h e cooked crabs are dipped in clean fresh water after w h i c h the pickers remove the m e a t from t h e b o d y sections b y shaking. A small wooden mallet is used to b r e a k the shells on the legs and claws so that the meat can b e removed. T h e b o d y and leg meats are kept separate. T h e m e a t is then p l a c e d in a flotation tank containing 1 0 0 ° salinometer brine. T h e m e a t floats in this solution, while any fragments of shell sink to the bottom. After further cleaning the m e a t is dipped in p H 2.8 solution of citric acid, rinsed in clear fresh water, and dipped in 8 0 - 1 0 0 ° salinometer brine solution. T h e m e a t then has a p H of 6.7 w h i c h prevents subsequent oxidation of t h e canned meat. I t is drained and pressed to remove excess moisture.
(it) Processing. T h e crab m e a t is p a c k e d in J ^ - and >4-lb. ( 0 . 1 1 and 0.22 k g . ) flat cans w h i c h contain 3% and 6 oz. drained meat, respec-
3 1 0 EIICHI TANIKAWA AND SHAMSUD DOHA
lively. All cans are lined in sea-food formula C-enamel. In t h e %-\b.
can, a layer of leg m e a t is p l a c e d on top of a layer of body meat. In t h e }i-lb. can, a layer of leg m e a t is laid at the bottom and top with b o d y m e a t at the center. T h e filled cans are inspected and spot-weighed.
T h e y are then passed on a conveyor to the v a c u u m closing and sealing machines.
T h e y are p a c k e d in retort baskets and processed at a temperature of 2 3 0 ° F . ( 1 1 0 ° C . ) for 8 0 min. T h e y are then immediately cooled, carefully examined, cleaned, labeled, and p a c k e d in fiberboard cases ( D e w b e r r y , 1955, 1 9 5 9 b ) .
c. JAPAN
T h e history of manufacture of c a n n e d crab in J a p a n is old; it started about 1 8 9 2 - 9 3 in the neighborhood of Otaru in Hokkaido ( T a n i k a w a , 1 9 5 3 ) .
T h e packing takes p l a c e either on board a floating cannery or on land.
T h e procedures in b o t h cases are similar.
( i ) Preparation. T h e crabs are captured b y tangle nets ( b o t t o m gill n e t s ) and have the c a r a p a c e removed on the fishing boats while returning to the cannery (floating or on s h o r e ) .
I f the c a r a p a c e is not removed, the enzymic action of the liver con
tained in t h e c a r a p a c e will b r e a k down the c r a b shoulder meat. This reduces substantially the p e r c e n t a g e of m e a t obtained after cooking.
T h e shelled carcasses are put into netting bags of about 1.5-inch m e s h and h e a t e d in boiling sea w a t e r about 1 8 - 2 0 min. for large ones ( h a r d c r a b ) w h e n 2 0 0 carcasses are treated at a time, or about 1 7 - 1 8 min. for small carcasses with each b a t c h comprising more than 3 0 0 carcasses. W h e n the freshness has declined somewhat the boiling should be increased 3 min.
T h e iron boiling vats are square in shape ( 5 . 0 χ 5.0 χ 5.5 ft.) and are heated b y steam.
T h e carcasses are removed from the cooking vat and cooled in cold sea water for about 10 min. After cooking, the meat is easier to separate from the shell. I t is done b y knife or scissors. T h e m e a t obtained b y knife is 1 0 - 2 0 % less than that b y scissors.
T h e m e a t separated from the shell is divided into body meat (shoulder m e a t ) , first leg meat, joint meat, second leg meat, and claw m e a t and put into separate pans and kept as such until p a c k e d in the cans.
After separation of m e a t from the shell, the m e a t is transferred to b a m b o o washing cages and washed in a tank of sea water.
After washing, the b o d y ( s h o u l d e r ) m e a t usually holds its shape.
Misshapen body and leg m e a t is degraded to "flake meat." T h e first leg m e a t is cut into segments equal to the height of the can. T h e joint and second leg meats also usually hold their shapes. T h e misshapen m e a t is used for the ornamental m e a t of the "third-grade style" canned crab.
T h e flake m e a t absorbs considerable sea water. T h u s the m e a t is graded into "fancy," "fair," "third" ("passed A, B " ) styles.
(it) Processing. Prepared c r a b m e a t is usually p a c k e d in a parch
ment-lined C - e n a m e l e d *4-lb. flat tin can, of w h i c h the net weight is about 2 3 0 g. Occasionally a p a c k e r will use }i- or 1-lb. flat cans for special markets.
I n preparing fancy style cans, 2 - 4 large pieces of the first leg m e a t are used for the top and bottom layers in order to give a good appear
ance, and the shaped shoulder meat, joint meat, and claw m e a t are placed at the sides. F l a k e m e a t is p l a c e d in the center.
According to J a p a n e s e inspection regulations, the weight of the m e a t in % - l b . flat cans of fancy class must b e above 1 8 5 g., of w h i c h the first leg m e a t ( 2 - 4 p i e c e s ) must amount to 5 3 g. and flake m e a t less than 5 5 g. T h e rest is shoulder, joint, and claw meat. T h e fair grade is the cans m a d e as fancy style, b u t with only fair quality meat. T h e third style is the cans in w h i c h the m e a t weight is above 185 g. and second or third leg m e a t or the broken m e a t ( n o t flake m e a t ) is p l a c e d in the top and bottom layers of the contents.
Since sea water is used for washing and boiling in floating canneries, the addition of salt is not necessary, b u t w h e n fresh water is used in land canneries, salt must b e added to about 2 g. per % - l b . can.
After the m e a t is p a c k e d in the can, the tops are clinched and vacuum- sealed. T h e sealed cans are p l a c e d in a retort w h e r e processing takes p l a c e for 8 0 min. at a temperature of 2 2 7 - 2 2 8 . 5 ° F . ( 1 0 8 - 1 0 9 ° C ) ; ( 5 . 0 - 5.5 lb. p r e s s u r e ) .
After the processing, the cans must b e cooled quickly in a spray of cold water. After cans are examined b y the striking sound, they are p a c k e d in wooden or fiberboard cases holding 9 6 or 4 8 >^-lb. flats.
d. H A I R C R A B ΓΝ JAPAN
Hair c r a b ( k e - g a n i ) is processed at land canneries in Japan. T h e re
moval of the c a r a p a c e from the c r a b b o d y is similar to that in the Alaska king crab. T h i s c r a b used to b e called the horse hair crab.
(i) Preparation. Carcasses from w h i c h the carapaces have b e e n removed are cooked in boiling water, fresh water (salt a d d e d ) , or sea water for 1 5 - 1 8 min.
After cooking the carcasses are quickly cooled. T h e shell of each leg is cut at three places with a large knife. O n e side of the shell of
3 1 2 EIICHI TANIKAWA AND SHAMSUD DOHA
the first leg is chipped b y the knife and the m e a t is removed b y shaking.
T h e m e a t of the second leg is removed from the shell b y using a bottle as a roller press. This m e a t breaks and b e c o m e s "red flake meat." T h e misshapen shoulder m e a t b e c o m e s "white flake meat."
T h e hair crab m e a t must b e more carefully washed than the king crab m e a t in order to prevent the appearance of blue discolorations.
T h e muscle fiber of hair c r a b is thinner than that of king c r a b and more likely to crumble. After removing the m e a t from the shell, the shaped and broken meats must b e separated and the off-color parts removed. T h e broken m e a t is white or red flake meat.
(it) Processing. Hair crab m e a t is generally p a c k e d in parchment- lined C-enameled ^2-lb. or }4 -lb. flat tin cans. T h e net weight of the m e a t in the y2-lb. flat tin cans is about 2 3 0 g. F r o m 4 to 6 pieces of the first leg m e a t are placed in the top and b o t t o m layers. B e t w e e n the top and bottom layers, white flake m e a t is p l a c e d outside and red flake m e a t on the inner side. T h e ratio o f white and red flake meats should b e 6 : 4 . W h e n fresh water is used for washing and cooking, salt must b e added in packing the meat. T h e grades of canned hair c r a b are divided into "fancy" and "choice" classes.
T h e processing takes p l a c e for 9 0 min. at a pressure of 5.0-5.5 lb.
and 2 2 7 - 2 2 8 . 5 ° F . ( 1 0 8 - 1 0 9 ° C ) .
2. Precautions in Crab Canning
T h e flavor of c r a b m e a t is delicate. I f freshness of the m e a t is reduced, the flavor and odor will b e affected. T h e r e f o r e the crab m e a t material should b e fresh. T h e b e s t m e t h o d for detecting freshness of crab m e a t is the estimation of the amount of volatile b a s e nitrogen ( V B N ) . W h e n the freshness of c r a b m e a t drops to incipient spoilage, the amount of V B N b e c o m e s 2 0 m g . % ( T a n i k a w a et al, 1 9 5 3 c ) . W h e n the value is b e l o w 10 mg. V B N / 1 0 0 g. meat, the cooked m e a t generally shows 15 mg. V B N / 1 0 0 g. meat. W i t h a range 1 0 - 2 0 mg. V B N / 1 0 0 g. in the raw meat, the cooked m e a t shows 1 0 - 1 3 mg. V B N / 1 0 0 g. meat. W h e n the V B N value is a b o v e 2 0 mg. V B N / 1 0 0 g. meat, even if the raw m e a t is cooked and processed for canning without delay, good quality canned crab is not obtainable. W h e n the amount of V B N rises above 2 5 m g . / 1 0 0 g.
m e a t it b e c o m e s unsuitable for canning ( T a n i k a w a , 1 9 5 9 ) . I f t h e fishing ground is far from the cannery, the carapaces must b e removed from the crab bodies on b o a r d the fishing boats prior to returning to the cannery. W h e n the carcasses arrive at the cannery, they are washed with sea water or dilute brine and immediately boiled. I f the carcasses are boiled without washing, the white portions of the m e a t m a y b e c o m e soft and show brownish or bluish discoloration.
T h e carcasses w h i c h are put into the boiling w a t e r should b e heated
evenly. W h e n four netting bags in w h i c h carcasses are put are dipped into the boiling water the penetration of the h e a t into carcasses is apt to b e c o m e unequal. F o r boiling, sea w a t e r or fresh w a t e r with salt
( 3 . 5 ° B e . ) should b e used. As t h e amount of soluble nitrogenous matter increases with e a c h boiling and lowers the quality of the product, the same w a t e r should never b e used m o r e than twice ( T a n i k a w a et al., 1 9 5 3 a ) . T h e boiling time must b e regulated according to freshness of the m e a t and size of the carcasses. I f the boiling time is inadequate, the m e a t will b e c o m e soft and dull in color. T h e autolytic action of enzymes is at a m a x i m u m in c r a b m e a t that has b e e n cooked at 1 4 0 ° F . ( 5 0 ° C ) , whereas it is destroyed in c r a b m e a t cooked at 1 9 4 ° F . ( 9 0 ° C . ) ( T a n i kawa, 1 9 5 9 ) .
T h e cooling of the carcasses must b e done immediately after the boiling. T h e rapid cooling firms up the m e a t and facilitates its removal from the shell.
Scrupulous clean-up in the cannery must b e carried out in order to prevent bacterial contamination. T h e boiling and washing w a t e r must b e of good quality and adequate. T h e cannery w a t e r m a y get contami
nated b y b a c t e r i a of the digestive system. T a n i k a w a et al. ( 1 9 5 3 b ) studied the fluctuation of Escherichia coli in cannery w a t e r and found that with the progress of canning operations the E . coli n u m b e r in t h e crab m e a t and the factory water increased, b u t after the heating during exhausting and sterilization the E . colt b a c t e r i a disappeared. Abnormal odor of the canned c r a b m e a t is often caused b y impure water. Insufficient supply of steam results in m e a t with b l u e discoloration as well as under- sterilization.
T h e sealing of the can must b e less firm than with other canned foods and the seam should b e thicker ( T = 5 8 - 6 0 / 1 0 0 0 i n c h ) . I f the closing is firm the surface of the C-enamel of the cans m a y crack, and the ferrous ion will dissolve from the b r e a k into the juice of the c a n n e d c r a b and combine with hydrogen sulfide generated from the c r a b m e a t during the processing. T h e n a b l a c k substance (ferrous sulfide) will appear at some part of t h e inner side of the cans a n d on t h e p a r c h m e n t paper.
After closing the cover of the cans, the cans must b e transferred to the retort very quickly. I f this cannot b e done the cans should b e dipped in chilled water with ice. I f the cooling is done slowly, glasslike crystals of struvite ( M g N H4( P 04) · 6 H20 ) will appear in the cans ( s e e further p. 3 1 6 ) .
3. Can Inspection
In J a p a n , c a n n e d c r a b for export must b e inspected on the basis of visual appearance of can contents after opening, texture, p a c k i n g style, and flesh color.
314 EIICHI TANIKAWA AND SHAMSUD DOHA 4. Problems
a. SHRINKAGE
Sometimes a shrinkage of the m e a t is encountered, generally taking p l a c e during the h e a t processing. This is linked with a toughening of the m e a t leading to abnormally low drained weights ( 8 6 . 7 % of n e t w e i g h t ) and rubbery or brittle and stringy texture. F ä r b e r ( 1 9 5 3 ) has shown that cooking the r a w crabs in salt water and using a 5 % sodium chloride solution to wash t h e cooked c r a b m e a t lead to minimal fluid uptake and result in less water loss during t h e heat sterilization.
b . BLACKENING
In early days c r a b canners suffered losses through the blackening of the canned crab meat. This discoloration was caused b y the hydrogen sulfide, evolved from S-containing proteins or other compounds during the heat processing, combining with ferrous ion dissolved from pin holes in the tin plate to form b l a c k ferrous sulfide ( T a n i k a w a and Yamashita, 1955; Y a m a d a and Tanaka, 1 9 5 9 ) . This reaction is accelerated b y the alkali of crab m e a t w h i c h has started to spoil.
T h e blackening can b e prevented b y addition of acid (e.g., tartaric or citric) in the can, b y lining the c a n with p a r c h m e n t paper, or b y using C-enamel-lined cans ( F e l l e r s and Parks, 1 9 2 6 ; L e g e n d r e , 1 9 2 8 ; Oshima, 1 9 2 7 ) . U n d e r a c i d conditions little hydrogen sulfide is formed from the meat. T h e other methods prevent the formation of ferrous sulfide b y keeping the hydrogen sulfide away from the iron ( B o u r y , 1953; N i e k e n , 1 9 5 5 ) .
c. B L U E DISCOLORATIONS
T h e blueing of canned c r a b m e a t has b e e n of concern to packers in b o t h J a p a n and the U n i t e d States. Numerous remedies have b e e n proposed. T h e s e include a patented aluminum salt treatment ( F e l l e r s and Harris, 1 9 4 0 ) for the Atlantic b l u e crab, and bleeding b y removal of the end appendages ( E l l i o t and Harvey, 1 9 5 1 ) for the Pacific D u n g e - ness crab. T h e b l u e m e a t often appears not only on the surface of c r a b m e a t in the can b u t also, though rarely, on c r a b m e a t several hours after boiling and cooking of the carcasses. B l u e i n g appears in canned hair crab m e a t ( k e - g a n i ) more often than in canned king c r a b .
T h e appearance of a b l u e discoloration of m e a t is due to hemocyanin, a copper-containing respiratory pigment in the blood of arthropods and molluscs ( D i c k and Pugsley, 1 9 5 0 ) . T h e more effectively b l o o d is re
m o v e d from the meat, the less the likelihood of blue discoloration. T h e blood remaining in the m e a t usually appears as a curdlike material, at first white b u t later showing extensive blueing. M e a t from parts of the
body with poor blood circulation such as the legs, claws, and joints often show very m a r k e d b l u e discoloration b e c a u s e of the difficulty of washing these parts effectively.
T h e usual m e t h o d employed commercially to minimize blueing is to rinse the p i c k e d m e a t in about 1 % solution of an acid such as citric, acetic, lactic, or tartaric. T h i s p r o b a b l y enables any c o p p e r present from remaining blood to c o m b i n e with the acid to form a weakly ionizing or nonionizing complex, w h i c h does not r e a c t as readily in forming a b l u e color during retorting. H o w e v e r , the acid treatment brings about m o r e extensive coagulation or denaturation of t h e m e a t proteins, with the result that the c r a b m e a t usually found in c o m m e r c i a l packs is often rubbery or brittle with loss of the texture and flavor of cooked fresh c r a b meat.
F ä r b e r ( 1 9 5 3 ) minimized these rather undesirable changes in the acid-treated m e a t b y treating t h e r a w m e a t with 1% sodium citrate in 5 % sodium chloride solution. T h e c a n n e d c r a b m e a t so treated was very similar to that of c o o k e d fresh c r a b meat, particularly in texture and flavor. B l u e discoloration was r e d u c e d in frequency.
O s a k a b e ( 1 9 5 7 , 1 9 6 1 ) s u c c e e d e d in preventing the a p p e a r a n c e of b l u e m e a t in t h e c a n n e d c r a b b y a low temperature and fractional heating o f the carcasses from w h i c h the c a r a p a c e h a d b e e n removed.
According to his experiments, t h e coagulating temperature of blood protein o f crabs is 6 & - 7 0 ° C , and that of m e a t protein o f crabs 4 3 - 6 5 ° C . I f the carcasses are h e a t e d to 6 0 ° C . the m e a t coagulates, b u t the blood is uncoagulated. After removing the m e a t from t h e c a r a p a c e in half-heated condition, the b l o o d generally drains out, leaving only the meat. W h e n this m e a t was boiled a f e w minutes in w a t e r containing alkali salt and p a c k e d in cans in the usual manner, t h e b l u e m e a t did n o t appear in t h e finished product.
This is the same m e t h o d used for c a n n e d tendonless ( b o n e l e s s ) c r a b meat. I n J a p a n , the introduction o f Osakabe's m e t h o d marks an epoch in the procedure o f canning c r a b meat.
d. ODOR
T h e odor of c a n n e d c r a b m e a t w h i c h has d e c o m p o s e d can b e classified into two kinds. O n e is like a combination of b u r n e d and soured rice. T h e cause o f this m a y b e the p a c k i n g of raw material not strictly fresh in w h i c h t h e glycogen has fermented. T h e other odor is that of ammonia. T h e cause of this is p r o b a b l y microbial decomposition of the c a n n e d meat. S u c h cans gradually develop swelling w h e n p l a c e d in an incubator. I n order to prevent these odors, q u i c k handling o f the raw material to avoid impaired freshness and meticulous sanitary precautions in the processing plant, machines, and other e q u i p m e n t are called for.
3 1 6 EIICHI TANIKAWA AND SHAMSUD DOHA
e. F L A T SOUR
T h e cause of the flat sour spoilage of canned c r a b was formerly said to b e due to thermophiles. T a n i k a w a et al. ( 1 9 5 6 ) , however, showed that the flat sour could also b e due to decomposition of the c r a b m e a t prior to the processing. B a c t e r i a formed in the crab m e a t w e r e in this case destroyed in the processing, b u t the organic acids were already formed, rendering a sour taste ( T a n i k a w a , 1 9 5 9 ) .
f. SWELLING
In order to preserve the good flavor of c r a b meat, a processing temperature of 2 2 7 - 2 2 8 . 5 ° F . ( 1 0 8 - 1 0 9 ° C . ) ( 5 . 0 - 5 . 5 l b . pressure) is recommended. T a n i k a w a et al. ( 1 9 5 2 , 1954a, b , c ) isolated the thermo- tolerant bacteria Bacillus subtilis var. mesentericus and B. megatherium from such swelled canned crab. W h e n the m e a t is fresh, even if a few such b a c t e r i a are in the c r a b meat, they are killed in the h e a t processing.
B u t extreme sanitary precautions are n e e d e d to obtain a good final product, thus avoiding lengthy cooking times.
g. STRUVITE FORMATION
T h e slow cooling of cans after retorting, or the bacterial action prior to or during storage, m a y cause the formation in the m e a t of struvite crystals of magnesium ammonium phosphate (Kizevetter, 1954; Fujii and Yamada, 1 9 5 6 ; Y a m a d a et al., 1 9 5 6 ; Y a m a d a , 1957a, b , c; see also Chap
ter 3, Section V , B , 5 , of this v o l u m e ) .
F e w e r struvite crystals w e r e formed in canned king c r a b m e a t w h e n it was h e a t processed at a lower temperature ( 8 0 ° C . ) rather than at 2 1 2 ° F . ( 1 0 0 ° C ) , and when it was sterilized at 1 0 8 . 4 ° C . at 5 l b . for 8 0 min. rather than at 7 lb. for 1 2 0 min. This crystal formation was effectively prevented b y adding about 0 . 2 2 % of sodium hexametaphos- phate ( Y a m a d a , 1957c, 1 9 6 1 ) . B y wrapping the m e a t (y2 l b . ) in parch
m e n t paper and adding 0 . 0 4 4 - 0 . 1 7 7 g. citric acid before canning, the crystal formation is likewise prevented (Anonymous, 1 9 6 1 ) .
h. BROWN DISCOLORATIONS
T h e color of normal commercial canned c r a b is generally white, but occasionally part of the white m e a t m a y b e c o m e brownish. This dis
coloration greatly reduces its market value. F ä r b e r ( 1 9 5 3 ) observed that browning, often referred to as scorching, is largely the result of faulty retorting practice. A definite brown discoloration is found only when the cans are removed from the retort while still hot and allowed to cool in the air. Prompt water cooling of the cans in the retort following the heat process yields a product with no significant browning of Dungeness c r a b meat.
N a g a s a w a ( 1 9 5 8 , 1959a, b , c, d, 1 9 6 0 ) m a d e a detailed study of the browning of c a n n e d king c r a b meat. H e has shown that the p a c k does not b e c o m e b r o w n w h e r e fresh material has b e e n used and subjected to high temperature boiling and then processed, whereas it always turned brown under these conditions when stale material has b e e n used. W h e n low temperature boiling is employed, the c a n n e d products b e c o m e brown irrespective of w h e t h e r the r a w material is fresh or not. I f either the free amino acids or the reducing sugars are r e m o v e d from the r a w c r a b meat, the finished product does not turn brown.
N-Glycosides w h i c h form in the initial stage of the Maillard reaction have b e e n separated from the b r o w n e d pack. A fluorescent substance and hydroxymethylfurfural, w h i c h are intermediate products o f the Maillard reaction, and melanoidins, w h i c h are the end products of t h e same reaction, have b e e n isolated from the b r o w n e d c a n n e d product.
T h e amounts of amino nitrogen and reducing sugars in a b r o w n e d p a c k are generally larger than those in a normal pack. O n the contrary, the amounts of amino nitrogen, reducing sugars, and c o p p e r in t h e exudates of b r o w n e d c a n n e d products w e r e less than those in normal cans. B r o w n i n g has m o r e often b e e n observed in the c a n n e d product prepared from h a r d shell c r a b than in that prepared from p e e l e d crab.
T h e b r o w n e d product shows fluorescence under ultraviolet light, the degree of browning b e i n g proportional to the degree of fluorescence of the meat. W h e n b o i l e d c r a b m e a t showing fluorescence is processed into c a n n e d products, the m e a t always b e c o m e s brown.
In addition to t h e d e g r e e of freshness of the r a w material and the boiling methods, as well as the conditions of the meat, t h e browning p h e n o m e n a are influenced b y the following factors: ( 1 ) p r e s e n c e of m e t a l ions in t h e pack, e.g., c o p p e r in blood and iron in m e a t ( a c c e l e r a t e s b r o w n i n g ) ; ( 2 ) b l o o d in t h e m e a t due to inadequate b l e e d i n g ( t h e m o r e blood, the greater the d e g r e e of b r o w n i n g ) ; ( 3 ) time lag b e t w e e n boiling and processing, particularly w h e n subjected to low temperature boiling ( t h e longer t h e lag, the greater the degree o f b r o w n i n g ) ; ( 4 ) processing temperature and time ( t h e higher the processing temperature or the longer the processing time, t h e higher the r a t e o f b r o w n i n g ) ; ( 5 ) p H o f the m e a t ( i f the boiled m e a t put into cans is acidic, the c a n n e d m e a t will b e c o m e white; in contrast, i f it is on the alkaline side during canning, the p a c k b e c o m e s b r o w n ) .
T o prevent browning, the following procedures have b e e n r e c o m m e n d e d : (i) improvement of handling a n d processing methods o f the c r a b carcasses so as to k e e p them in a fresh state until they are landed and processed, (ii) improvement of the boiling methods, and (Hi) dis
carding the boiled m e a t showing fluorescence.
318 EIICHI TANIKAWA AND SHAMSUD DOHA 5. Crab Catches and Size of Pack
L a n d i n g statistics of crabs ( F A O , 1 9 6 1 ) shows that the United States leads in c r a b fishing with 114,000 metric tons in 1 9 6 1 in w h i c h b l u e crab represents 65,000, Dungeness crab 15,000, and king crab 19,500 metric tons. Next comes J a p a n with 63,000 metric tons in w h i c h king crab represents 27,000 and zuai crab 13,000 metric tons. T h e U.S.S.R. occupies third p l a c e with 38,700 metric tons, all of w h i c h is king crab. Thus in the case of king crab the Soviet Union occupies first place.
T h e canning of b l u e c r a b is almost nil in the United States. Pre
sumably the U.S.S.R. leads in the canning of king crab b u t the size of p a c k is not available; it is assumed that the entire catch is processed.
TABLE la
CANNED CRAB PRODUCTION
(in 1000 metric tons)
Country 1956 1957 1958 1959 1960 1961
Japan 7.0 6.2 4.0 5.9 6.8 7.4
United States 1.2 1.5 1.4 1.4 2.0 2.0
a Yearbook of Fishery Statistics (FAO), Vol. 14, 1961.
T a b l e I shows the quantity of canned crabs produced in J a p a n and the United States from 1 9 5 6 to 1 9 6 1 .
B . LOBSTERS
T h e following lobsters are economically important:
C a n a d a and United States: Northern lobster (Homarus americanus);
spiny lobster (Panulirus argus, P. interruptus).
J a p a n : Spiny lobster (Panulirus japonicus).
W e s t e r n E u r o p e : Norway lobster (Nephrops norvegicus); lobster (Homarus vulgaris).
South and Southwest Africa: R o c k lobster (Jasus Mandii).
O c e a n i a : R o c k lobster (Jasus Mandii, J . verreauxi).
C a n a d a is the leading lobster fishing country in the world with an annual average of 21,700 m e t r i c tons during 1 9 5 9 - 6 1 , the United States b e i n g second with 13,300 metric tons. T h e Canadian lobster fishery is centered in Nova Scotia and Newfoundland, while that of the United States is along the coast of N e w E n g l a n d .
E u r o p e a n lobsters are caught chiefly in F r a n c e and the United Kingdom. I n the former the c a t c h was 8 4 0 0 metric tons and in the latter 3 7 0 0 metric tons in 1 9 6 1 . Catches of other lobsters in other countries are of minor importance.
C a n a d a is presumably t h e leading country as to lobster canning, with an average o f 9 0 0 m e t r i c tons during 1 9 5 & - 6 1 .
1. Canning Northern Lobster a. CANADA
The live lobsters a r e killed b y dipping into a boiling 3 % brine. After boiling for 2 0 - 3 0 min. they a r e cooled in cold salt solution. T h e claws and tail a r e broken off, a n d t h e b o d y shell is opened, t h e offal removed, a n d t h e m e a t taken out o f t h e shell. T h e claws a r e cracked a n d t h e m e a t removed whole, i f possible. T h e arms a r e split longitudinally a n d t h e m e a t taken out with a fork. T h e tails are split a n d the intestines removed.
In filling t h e cans, tail m e a t is usually p l a c e d a t t h e b o t t o m a n d t h e arm a n d claw m e a t o n top. A n 8 % brine is a d d e d which gives a final concentration o f about 2 % salt i n t h e c a n n e d lobster. Occasionally t h e m e a t is flavored with pepper, b a y leaves, a n d cloves. E a c h b a t c h of unsealed cans is p l a c e d in a n exhaust b o x o f t h e water b a t h or steam type a t 2 1 2 ° F . ( 1 0 0 ° C ) . This obviates t h e formation o f flippers or springers and reduces strain on t h e seams during processing. T h e exhaust treatment also reduces t h e c h e m i c a l changes causing deterioration in color a n d flavor during storage. T h e cans a r e sealed while still h o t a n d p r o c e s s e d in retorts a t 2 3 9 ° F . ( 1 1 5 ° C . ) for 2 5 , 2 9 , or 4 0 min., r e s p e c t i v e l y , for cans o f 3 , 6 , a n d 1 2 oz. After processing, t h e cans a r e immediately c o o l e d t o 1 0 0 ° F . ( 3 8 ° C . ) .
b . UNITED STATES
The selected lobsters, usually under 9 inches in length, a r e dropped alive into a tank o f boiling water containing 3 - 5 % salt. T h e cooking time r e c o m m e n d e d is 1 5 - 3 0 min. from t h e time t h e w a t e r starts to reboil; t h e actual time allowed depends on t h e quantity b e i n g cooked a n d t h e size of t h e lobsters. L a r g e canneries cook in lots o f 5 0 0 l b . in live steam for 1 5 min. a t pressures o f 5 - 1 0 l b . / s q . in.
After cooking, the lobsters a r e cooled in a water spray or b y lowering into tanks o f w a t e r containing 5 - 6 % salt. Salt a d d e d i n cooking acts as a flavoring agent a n d serves also to m a k e t h e flesh somewhat firmer in texture. T h e lobsters, after cooling, a r e piled on dressing tables where the tail a n d claws a r e pulled off, t h e b o d y split open, a n d t h e offal removed. T h e m e a t is p i c k e d out b y hand, using a specially designed heavy knife. T h e tail is so c u t that t h e m e a t m a y b e removed in a f e w large pieces, t h e claws a r e cracked, a n d t h e m e a t is pulled out with as little b r e a k a g e as possible. T h e flesh from t h e legs is p i c k e d out in small pieces. T h e m e a t is sorted as p i c k e d a n d e a c h grade k e p t separate.
T h e p i c k e d m e a t is cleaned o f shell or offal a n d washed thoroughly
320 EIICHI TANIKAWA AND SHAMSUD DOHA
in running water but not allowed to soak. After draining, it is dipped in brine containing a small amount of organic acid; this is usually citric, though acetic m a y also b e used. T h e acid treatment reduces or prevents darkening of the flesh caused b y the formation of iron sulfide. T h e amount of acid used should not allow an acid flavor to b e d e t e c t e d in the canned product.
Cans with sulfur-resistant lacquer and p a r c h m e n t paper lining are used. Tail m e a t is placed on the bottom, small pieces of leg in the center, and claw m e a t on top; 7 oz. m e a t are necessary to secure a cut
out weight of 6 oz. A small amount of salt is added to e a c h can. This preserves the flavor in the c a n n e d product and aids in reducing any darkening of the m e a t caused through overprocessing.
Covers are clinched loosely on the filled cans, w h i c h are exhausted for 9 - 1 2 min. at 2 1 0 - 2 1 2 ° F . in hot water or in steam exhaust boxes before b e i n g sealed. Half-pound cans with 7-oz. fill of m e a t are retorted at 2 4 0 ° F . for 4 5 min. and 1-lb. cans with 12-oz. fill of m e a t for 7 5 min.;
they are water cooled immediately (Jarvis, 1 9 4 3 ; M o n t g o m e r y and Prater, 1 9 6 3 ) .
Analyses of canned lobster for magnesium, ammonia, and inorganic and total phosphorus indicate that the extent of crystallization of struvite in canned lobster is limited b y the magnesium concentration. Hollett ( 1 9 4 3 ) has shown b y experimental canning that sea water, whose magnesium concentration is approximately 5 times that of lobster meat, is the major controlling factor in the formation of large quantities of these crystals. Formation of the crystals in c a n n e d lobster can b e almost completely eliminated if sea water is not used in any step of the canning procedure.
2. Canning Rock Lobster a. SOUTH AND SOUTHWEST AFRICA
R o c k lobster (Jams Wandii) is a large-tailed sea crawfish. I t is pre
cooked for 1 5 min., soaked in running sea water for about 15 min., and drained effectively prior to filling of the cans (Dreosti, 1 9 4 9 ; Dreosti and van der M e r w e , 1949a, b , c, d ) .
T h e precook results in substantial loss of weight ( L e R o u x et al., 1951, 1 9 5 2 ) . T h e tail with shell represents 3 0 - 4 0 % of the weight o f the cooked product.
b . DlSCOLORATIONS
L e a c h i n g the fresh m e a t in water at 6 0 ° F . ( 1 6 ° C . ) and at 1 2 0 ° F . ( 4 0 ° C . ) results in normal canned products b u t those leached at 2 1 2 ° F . ( 1 0 0 ° C . ) b e c o m e dark in color. Pretreatment of the flesh with various
organic acids to reduce the p H below 6.4 before canning often reduces the tendency for the flesh to develop the gray, black, and blue dis- colorations due to reactions b e t w e e n copper in the blood and sulfide and ammonia in the tissues ( M o n t g o m e r y and Prater, 1 9 6 3 ) .
B r o w n i n g develops during storage b y a Maillard reaction b e t w e e n sugars and amino acids in the muscle. This can b e diminished b y soaking the m e a t in clear running sea water for 15 min. before canning. H i g h processing temperature and short processing time ( 5 2 min. at 2 4 0 ° F . , 1 1 5 ° C . ) , diminish the risks of browning and the product generally remains white even after 4 months of storage.
c. STRUVITE FORMATION
This crustacean also develops struvite crystals ( s e e a b o v e ) . B y lowering the p H of m e a t to 6.4 or less, with l a c t i c or citric acid, it can b e com
pletely avoided. T h e addition of 0 . 5 % sodium hexametaphosphate is another w a y o f preventing formation of these crystals during storage.
C. SHRIMPS AND PRAWNS
T h e following shrimps and prawns are economically important:
U n i t e d States, Canada, and M e x i c o : Shrimps (Penaeus setiferus, P. duorarum, P. aztecus, P. brasiliensis, Xyphopeneus kroyeri, and Pan- dolus s p p . ) .
J a p a n : Shrimp (Pandalus kessleri, P. hypsinotus, and P. borealis);
K u r u m a prawn (P e n a e u s japonicus).
W e s t e r n E u r o p e : C o m m o n prawn (Leander serratus); deep-water prawn (Pandalus borealis); c o m m o n shrimp (Crangon vulgaris).
Australia: Prawns (Metapenaeus monoceros, M. macleayi, and P.
esculentus).
L a n d i n g statistics of shrimps and prawns ( F A O , 1 9 6 1 ) show that the United States, with an average of 100,000 m e t r i c tons during 1 9 5 9 ^ 6 1 . Other leading countries are India, J a p a n , and Mexico.
1. Canning Shrimps a. UNITED STATES
(/) Preparation. W h e n the raw shrimp are landed at the cannery, they are inspected. T h e n they are unloaded into a metal washing tank.
T h e shrimp sink and are carried out o f the tank on a conveyor b e l t into a revolving drum to remove surplus water and any debris, such as seaweed.
F r o m there they are carried to the sorting conveyor w h e r e the broken, soft, torn, discolored, or otherwise defective shrimp are removed. T h e y fall from the end of a conveyor into a basket or metal lug box.
T h e baskets or lug boxes are taken directly from the sorting b e l t to
322 EIICHI TANIKAWA AND SHAMSUD DOHA
the picking room. Shrimp are peeled entirely b y hand, and the m e a t is inspected. T h e m e a t is now washed and the drained m e a t dipped into a tank of boiling 5 0 ° salinometer brine.
I f the shrimp are to b e canned "wet pack" they are b l a n c h e d for 8 - 1 0 min., varying with size, or 1 0 - 1 2 min. i f "dry p a c k " shrimp are being prepared. After blanching the shrimp are cooled and dried in a current of air for about 3 min.
T h e dried shrimp are n o w inspected and graded. T h e n u m b e r of shrimp filled into the can is the most important factor in grading. No. 1 picnic cans are used for the largest p a r t of the pack. I f w e t p a c k shrimp are canned, the drained weight must b e 5 % oz.; dry p a c k in No. 1 cans must have a net weight of 5 oz. and a fill-in weight of 5 ^ oz., since there is a slight shrinkage in the method of processing.
W e t p a c k shrimp are sealed immediately b y a closing machine. D r y p a c k m a y b e given a m e c h a n i c a l vacuum seal.
(it) Processing. W e t p a c k shrimp in No. 1 cans are processed 2 0 min.
at 2 4 0 ° F . ( 1 1 5 . 7 ° C . ) ( 1 0 lb. pressure), or 1 0 min. at 2 5 0 ° F . ( 1 2 1 . 1 ° C . ) ( 1 5 lb. p r e s s u r e ) . No. V/2 cans are processed 2 3 min. at 2 4 0 ° F . or 12 min. at 2 5 0 ° F . D r y p a c k shrimp in No. 1 cans are processed 8 5 min. at 2 4 0 ° F . or 6 0 min. at 2 5 0 ° F . if the can is lined with one-piece parchment liner. I f there is no liner or i f a three-piece liner is used, the process is 7 0 min. at 2 4 0 ° F . or 5 3 min. at 2 5 0 ° F .
After processing the cans are chilled to 9 8 ° F . before warehouse stacking (Jarvis, 1 9 4 3 ) .
A considerable amount of U.S. shrimp is b e i n g p a c k e d in glass.
Several sizes of glass container are used. T h e shrimp are p a c k e d in 3 % brine and filled hot at temperatures of 1 6 0 - 1 8 0 ° F . ( 7 1 - 8 2 ° C . ) . T h e jars are vacuum-closed.
F o r glass containers size 5 - 9 oz. a processing time of 2 2 min. at 2 4 0 ° F . ( 1 0 lb. pressure) or 14 min. at 2 5 0 ° F . ( 1 5 lb. pressure) is prescribed (Jarvis, 1 9 4 3 ) .
b . JAPAN
I n Japan, Pandalus borealis is p a c k e d as canned shrimp. T h e animals are picked or p e e l e d b y hand. First, the shrimp head as well as the yellow substance attached to it is removed, then the carcasses are washed. T h e shrimp are b l a n c h e d in a b r i n e — 6 - 9 ° B a u m e ( 2 4 - 3 6 ° salinometer)—for 2 - 3 minutes. T h e m e a t is then picked from the shell.
T h e b l a c k streak tissue attached to the upper side of the m e a t is removed.
T h e m e a t is soaked in an acid solution ( 1 lb. tartaric acid dissolved in 10 gallons of w a t e r ) for about 15 min. T h e m e a t is washed, drained, and steamed for about 1 5 - 3 0 min. Steaming makes the m e a t red and renders
a comma-shaped product. T h e m e a t is then partially dried, b u t in the shade. D i r e c t sunlight induces odors.
This drying procedure is important, otherwise the shrimp would stick together in t h e can. After size grading and filling in parchment-lined and C-enameled cans, there is n o exhausting.
D r y - p a c k shrimp are processed for 9 0 min. at 2 2 7 ° F . ( 1 0 8 ° C ) . A small quantity of brine of 6 ° B a u m e ( 2 4 ° salinometer) is a d d e d to each can in the case of wet-pack. T h e s e are processed for 1 8 - 2 0 min. at 2 2 7 ° F . , depending on can size.
2 . Special Features a. DISCOLORATIONS
B l a c k e n i n g m a y also occur in shrimp ( B o u r y , 1 9 5 3 ; Nielsen, 1 9 5 5 ) . Methods of prevention are the same as those for c r a b ( s e e a b o v e ) .
T h e typical orange-red color declines after long storage of cans. W h e n the r a w product is decomposed prior to canning, this color changes to a yellow-brown ( B a r r y et al., 1 9 5 6 ) . T h e shrimp m a y also turn gray and blue ( L a n d g r a f , 1 9 5 6 ) .
T h e p H o f the canned product increases with the length of time the shrimp are held on i c e . T h e r e is an increase in p H prior to spoilage. T h i s c h a n g e in p H enhances gray discolorations. T h e m e t h o d of peeling w h e t h e r b y h a n d or b y m a c h i n e has no effect on these discolorations.
In order to prevent these discolorations, the shrimp should b e dipped in a citric acid brine in order to r e d u c e the p H of the finished product to b e l o w 6.4.
b . SOFTENING
T h e cause of the softening of c a n n e d shrimp is the decomposition of the protein to soluble nonprotein, w h i c h usually occurs in the raw material as the freshness declines. I n order to prevent softening of canned shrimp meat, strictly fresh r a w material should b e employed and sanitary conditions in t h e cannery must b e carefully maintained.
3. Manufacture
T a b l e s I I and I I I show the insignificant quantities that are canned.
TABLE II PACK OF CANNED SHRIMP
(in 1000 metric tons)
1956-58 1959-61
Country (average) (average)
United States 5.8 5.7
West Germany 2.8 2.2
Others 0.2 0.6
3 2 4 EIICHI TANIKAWA AND SHAMSUD DOHA TABLE III«
PACK OF CRUSTACEANS0 PRODUCED IN PRINCIPAL COUNTRIES (in 1000 metric tons)
Country 1 9 5 6 - 5 8 1 9 5 9 - 6 1
United States 7 . 3 7 . 8
Japan 6.1 7 . 0
West Germany 2 . 9 2 . 2
Norway 1.3 2 . 6
Canada 1.4 1.1
Sweden 0 . 3 0 . 3
Others 4 . 1 1.4
Total 2 3 . 4 2 2 . 4
a Yearbook of Fishery Statistics (FAO), Vol. 14, 1 9 6 1 .
0 Crabs, lobsters, shrimps, prawns, etc.
III. Molluscan Shellfish
A. OYSTERS
T h e following oysters are economically important and heat processed in cans:
United States: Pacific oyster (Östren gigns); Atlantic oyster (Östren virginica).
J a p a n : Oyster (Crassostrea laperousei, Ostren rivularis, O. denselamel- losa, and O. gigns).
T h e United States leads in the c a t c h of oysters, with an annual average of 4 0 0 , 0 0 0 metric tons during 1 9 5 9 - 6 1 . Next comes J a p a n with an annual average of 168,000 metric tons during t h e same period.
Oysters can b e raised b y artificial cultivation. T h e Japanese are perhaps the oldest oyster farmers, b u t the R o m a n s w e r e growing oysters in L a k e Lucrinus near Naples in 9 5 B . C . Oyster farming started in the United States in 1867 ( M e d c o f , 1 9 6 1 ) .
1. Canned Pack a. UNITED STATES
T h e heat processing of oysters started in the United States as far b a c k as 1820.
T h e r e are two methods employed in the United States, one used in the southeastern Atlantic coast and Gulf states and the other on the Pacific coast. T h e canneries on the Atlantic and G u l f coasts use wild- grown oysters harvested from public reefs. T h e stock delivered to canneries frequently contains a large proportion of undersized and young oysters. W i t h o u t washing of shells they are unloaded directly into cars with a capacity of 5y2 barrels ( 2 2 b u s h e l s ) each. T h e loaded cars are run into a steam b o x and steamed for 1 0 - 1 5 min. at 2 4 5 ° F . ( 1 1 8 ° C . ) ( 1 2 lb.
p r e s s u r e ) . Under steaming, the shells open and lose a great portion of juice. T h e cars are then rolled into a shucking room a n d the m e a t is removed while hot. After b e i n g dropped into a galvanized flume, the m e a t is forced b y a stream of cold water to the washing tanks where a considerable quantity of grit and shell particles is washed out or trapped by baffles. W a s h i n g continues 2 0 - 3 0 min.; then the m e a t is transferred b y dip nets to screen-bottomed trays, in w h i c h they are left to drain for 2 0 min. After inspecting and grading, filling takes place. H o t 1 % b r i n e is added and the cans are sealed. T h e following processing times are practiced.
Time Degree 5-oz cans 17 min. 240°F. (116°C.)
Others 19min. 240°F. (116°C.) 10 min. 250°F. (121°C.) Pacific oysters used in canning are grown from imported J a p a n e s e seed, planted on privately owned beds. After washing under pressure they are m o v e d to a steam chest for precooking. T i m e and temperature of precooking are 3 . 5 - 6 min. at 2 4 0 ° F . ( 1 1 6 ° C . ) ( 1 0 lb. pressure) and 1 0 - 1 5 min. at 2 1 2 ° F . ( 1 0 0 ° C . ) ( a t m o s p h e r i c p r e s s u r e ) . T h e oysters are sucked into 3-gallon buckets containing 1 gallon of w a t e r or 2 - 3 % brine.
S o m e canneries prefer to use a continuous precooker. Precooked oysters are removed from the shell with a knife and p l a c e d for washing in a metal tank with a perforated false bottom. After thorough washing, aided b y aeration or blowing, the shucked oysters are emptied into a conveyor and sorted into four size grades.
After exhausting and sealing, the cans are processed at 2 4 0 ° F . ( 1 1 6 ° C ) . T h e duration of heat processing is 2 0 - 4 2 min., depending on can size (Galtsoff, 1 9 5 1 ) .
b . JAPAN
Ostrea (Crassostrea) gigas, O. denselamellosa, and O. (Crassostrea) rivularis are used in J a p a n e s e oyster packs. Only large, fat, and well- shaped specimens are used.
(/) Processing. Oysters shucked in the raw condition are generally washed with 2 - 3 % salt solution, drained, and steamed 1 0 - 1 5 min. at 2 1 2 ° F . ( 1 0 0 ° C ) . Oysters in the shell are treated as in the United States.
T h e m e a t is removed from the shell while hot, washed carefully, and drained. After inspection and grading of the steamed, washed, and drained meats, they are p a c k e d in cans; 1 - 2 % brine is a d d e d and the cans are sealed and processed.
(it) Smoked oyster in oil. T h e harvested oysters are shucked b y hand. T h e meats are p l a c e d in barrels and taken to the cannery. T h e
3 2 6 EIICHI TANIKAWA AND SHAMSUD DOHA
mucous substance on the surface of the b o d y is removed b y sprinkling 3 - 6 % salt and allowing to stand about 2 hr. T h e n they are carefully washed in fresh water agitated b y air under pressure, a n d boiled for 3 min. to m a k e the m e a t firm. Steaming is the next step, 2 0 min. at 2 1 2 ° F . ( 1 0 0 ° C . ) or 1 0 - 2 0 min. at 2 1 5 ° F . ( 1 0 1 . 8 ° C ) . After cooling they are placed in a smoking room and smoked for 2 0 - 4 0 min. at 1 2 2 - 1 7 6 ° F . ( 5 0 - 8 0 ° C ) . Various sized cans are used. H e a t processing is generally for 6 0 min. at 2 2 9 ° F . ( 1 0 9 . 9 ° C . ) ( 6 lb. p r e s s u r e ) .
2. Precautionary Measures
T h e shucked meats must b e thoroughly washed to remove sand, mud, shell particles, etc. All discolored and otherwise defective meats are discarded ( H o m a n s , 1950c; Hardy, 1 9 5 2 ) . After steaming, the oyster bodies must b e handled very carefully.
TABLE I V PACK OF OYSTERS
(in 1000 metric tons)
1 9 5 6 - 5 8 1 9 5 9 - 6 1
Country (average) (average)
United States 6 . 0 5 . 7
Japan 1.7 4.2
C a n n e d oysters m a y exhibit swelling due to thermophilic b a c t e r i a ( K i m a t a and Akamatsu, 1 9 5 8 ) if the heat processing is inadequate.
T a b l e I V shows 3-year averages indicating the size of this pack.
B . SCALLOPS
T h e scallop is a mollusc belonging to the lamellibranch family Pectinidae. T h i s comprises about 4 0 species, four of w h i c h are found on the Atlantic coast of the United States. O f these only two are of com
mercial importance. T h e common shallow-water scallop, found from Massachusetts to the Gulf of Mexico, is the most important commercial species. This scallop is usually designated Pecten gibbus boreaiis, al
though it is also called Pecten Aequipecten irradians. In E n g l a n d it is called "fan shell," "frill," "queen," and "squim." T h e giant deep-water scallop, found from N e w J e r s e y to Labrador, is Placopecten megeUanicus.
Several species of scallop are found on the Pacific coast of the United States ( T r e s s l e r and L e m o n , 1 9 5 1 ) . In J a p a n , the commercial species is Pecten yessoensis, w h i c h is present in the cold sea of Hokkaido and Mutsu B a y . Scallops are also found in F r a n c e and in Australia.
T h e scallop is canned only in Japan. In other countries it is sold fresh or frozen.
1. Canned Pack a. JAPAN
A b o u t 1 0 shells are h e a t e d at a time for 3 min. in boiling water. T h i s opens the shells. T h e b o d y is r e m o v e d and the adductor muscle, the
"eye," is cut out, b e i n g the most valuable part as food. T h e thin m e m b r a n e surrounding the muscle must not b e r e m o v e d in the washing, as the muscle fibers will b r e a k apart. After washing, the muscles are boiled in dilute salt solution for 1 5 min. After cooling they are filled into 1-lb.
or 0.5-lb. flat cans with 2 % brine solution, and processed for 7 0 min. at 2 3 0 ° F . ( 1 1 0 ° C . ) ( 6 lb. pressure) for the 1-lb. flat can.
Retention of shape and avoidance of browning are the chief problems in the canning of scallops. As mentioned above, disruption of the thin m e m b r a n e surrounding the adductor m u s c l e causes disintegration into fibrous pieces.
B r o w n i n g is generally caused b y either ( 1 ) heating the dry packs, or ( 2 ) using raw material not completely fresh. T h e r e f o r e excess heating must b e avoided and strict quality control of the raw scallops must b e observed.
C. ABALONES
T h e abalone, also called "sea ear" and "ear shell," belongs to a family of marine snails, the Haliotidae, of w h i c h eight species ( b l a c k , red, pink, green, northern green, threaded, J a p a n e s e , and Pourtales) are encoun
tered on the Pacific coast of the United States and C a n a d a ( Q u a l e , 1 9 6 2 ) , b u t not on the Atlantic coast. I n J a p a n and Korea, J a p a n e s e abalone (Haliotis discus hannai) and H. gigantea are caught.
1. Canned Pack a. UNITED STATES
After removal from the shell, the abalone is prepared b y cutting out the viscera and removing the b l a c k envelope around the foot. After washing, it is b r i n e d for about 4 8 hr.; the foot muscle is m i n c e d and filled into cans w h i c h are exhausted for 4 5 min. at low temperature. After sealing, t h e cans are heat processed for 1 hour at 15 lb. pressure ( T r e s s l e r and L e m o n , 1 9 5 1 ) .
b . JAPAN
T h e r a w abalone for canning must b e fresh and of a size such that there are 3 - 5 in a 1-lb. can. I t is r e m o v e d from the shell and the visceral mass and mantle fringe are trimmed off. After washing, it is dry salted for 1-2 nights with 0 . 1 - 0 . 1 5 kg. salt p e r 1.0 kg. meat. T h e n it is r u b b e d in order to remove dirty mucous substances, washed with fresh water
3 2 8 EIICHI TANIKAWA AND SHAMSUD DOHA
2 - 3 times, and left to soak for 1-2 hr. I t is then drained and p a c k e d in cans.
Another m e t h o d is to fill the cans before heating for 0 . 5 - 1 hr. in boiling water with y$ water, exhausting for 3 0 min. at 2 2 1 . 5 ° F . ( 1 0 5 ° C . )
( 3 lb. p r e s s u r e ) , and sterilizing under 8 lb. steam pressure for 1 hr.
c. SOUTH AFRICA
Dreosti ( 1 9 5 0 ) reported that canning of abalone (Haliotis midae) in South Africa is done b y dry salting ( 7 % b y w e i g h t ) the shelled product for 2 4 hr. or more, scrubbing, removing the mouths and fringes, desalting in lukewarm ( 1 0 0 ° F . , 3 8 ° C . ) water for 2 hr., splitting across the foot, folding, and packing with added water. T h e processing is for 75 min. at 2 4 0 ° F . ( 1 1 5 ° C . ) .
2. Precautionary Measures
Unless the m e a t has b e e n carefully washed, the j u i c e of the c a n n e d boiled abalone may b e c o m e turbid after a time. I f the raw product is p a c k e d in cans and processed directly it b e c o m e s extremely tough.
Prolonged retorting softens the flesh somewhat, but the color and flavor are adversely affected. Tenderizing to any desired degree can b e achieved b y gently pounding t h e flesh before canning. T h e cracking of t h e foot that is prone to occur during canning can b e avoided b y slicing off a thin (y in., 3 m m . ) layer prior to canning (Dreosti, 1 9 5 0 ) . B l u e discoloration m a y develop in the p a c k ( v a n der M e r w e , 1 9 5 5 ) . T h e methods of prevention are similar to those for crab ( s e e a b o v e ) .
D . C L A M S
Clams are one of the most popular and important shellfish in the world. T h e y are produced abundantly in Canada, the United States, Argentina, Chile, China, Japan, and Korea. Clams are classified into m a n y families and genera.
On the Atlantic coast of North America, surf or b a r clam (Mactra solidissima), soft clam (Myα arenaria), and hard clam or quahog (Venus mercenaria) are found. On the Pacific coast of the same continent, razor clams (Siliqua patula), butter clams (Saxidomus nuttali), little-neck clams (T a p e s staminea), and hard clams are abundant. On the coasts of Argentina and Chile, hard clams are caught. H a r d clams are found in China. In J a p a n there are m a n y species of fresh water clam (Corbicula leana), hard clam (Meretrix lusoria), hen clam (Spisula sachalinensis), short-necked c l a m (Venerupis japonica), and "mogai" (Anadara sub- crenata). Short-necked clams are also abundant in Korea.
Several species are canned b o t h whole and m i n c e d in Canada, the United States, and J a p a n .
1. Canned Pack a. UNITED STATES
Several species of clams (soft, hard, razor, e t c . ) are canned both whole and m i n c e d in the United States. T h e general procedure, except for the removal of the siphon, is similar for all species. In some canneries this is included with the whole meat.
( i ) Minced clams. In the United States, the m e a t of clams is removed by an automatic shucker and p l a c e d in large pans, dressed, and cleaned.
This is accomplished b y splitting the meats on one side with scissors. T h e dark mass near the end of the siphon containing sand and dirt is clipped off. T h e cut meats are washed in a special washing machine. T h e siphon and side walls are cut away from the washed meats and discarded, and the stomach is slit open and cleaned. T h e cleaned dressed meats are minced in a m e a t grinder. S o m e of the juice which runs out during the grinding is added to the cans. T h e cans are exhausted at about 2 1 0 ° F . ( 9 9 ° C . ) for about 8 min. with the lids loosely on. After sealing, the cans are processed at about 2 2 0 ° F . ( 1 0 4 ° C . ) ( 2 . 5 lb. p r e s s u r e ) . One-lb. cans are processed for 9 0 min., 0.5-lb. cans for 7 0 min.
(it) Clam nectar. During grinding of the clam m e a t a considerable quantity of liquid is expressed. Although some of the liquor is added to each can, a considerable surplus remains. This is canned separately and sold as clam nectar. T h e hot liquor is p l a c e d in 1-lb. cans which are then sealed and sterilized. I f the liquor is cold when canned, the cans are exhausted before sealing in the same manner as in the canning of razor clams. T h e 1-lb. cans of nectar are cooked in an autoclave for 1 hr. at 2 4 0 ° F . ( 1 1 6 ° C ) .
Clam liquor is also obtained from clams of the genus Donax, which are too small for utilization in any other way.
(tit) Clam chowder. C l a m chowder is usually prepared from the hard or quahog clam inasmuch as this clam possesses a pronounced clam flavor. I f milk is used as an ingredient, it is necessary to add small quantities of a citrate or phosphate to prevent curdling.
T h e proportions of ingredients, for example, are as follows: 2 5 0 0 quahog clams, 2 5 lb. bacon, 2 5 lb. white potatoes, 7 lb. onions, 2 5 lb.
tomatoes, lb- chopped parsley, τ/& lb. thyme, 1 oz. sweet marjoram, 1 lb. salt, τ/2 lb. ground white pepper, and 15 gallons water ( C o b b , 1 9 1 9 ) .
T h e clams are thoroughly washed, drained, and chopped; potatoes and b a c o n are diced; then all ingredients are boiled for 10 min., after w h i c h the chowder is filled into cans under stirring. T h e No. 3 cans are
