Extracting the Meats
Freezing and Cold Storage of Mussels
The mussel (Mytilus edulis) is eaten throughout Europe, and to a lesser extent in North America. It is a bivalve, that is the shell is in two separate halves, kept together by a powerful muscle. The shell is smooth, and blue-black in colour; young mussels are sometimes yellowish-brown with blue-black bands. Roughly oval in shape and rather pointed towards the hinge, the mussel reaches marketable size after about three years' growth, when it is two inches or more in length.
Mussels are either harvested from natural stocks, or are cultivated by relaying them for faster growth and for fattening, to be recovered later by rake or dredge.
The quality of the meats from mussels varies during the year. They are at their best in the late autumn and winter but become poor during and after spawning in March or April. Some Sea Fisheries Committees have byelaws preventing mussels being fished during certain summer months.
The edible part of the mussel contains approximately 80 per cent water, 9 to 13 per cent protein, 0 to 2 per cent fat and 1 to 7 per cent glycogen (animal starch) depending on the season. It has a calorific value of about 80 calories per 100 grammes wet weight.
Most European maritime nations gather and process mussels, but by far the greatest quantity is taken in the Netherlands; France, Denmark and Germany also produce considerable quantities.
Shells of fresh mussels are either tightly closed or will close when touched. If the shells are open or gaping, the mussels are dead or dying, and may well have an unpleasant smell.
Mussels are sometimes eaten raw or lightly cooked. Inshore waters are subject to pollution by sewage to varying degrees, and some microscopic algae on which the mussels feed may produce toxins. Consequently, as is the case with all bivalve molluscs and some other shellfish, consumption of mussels contaminated with pathogenic bacteria, viruses or algal toxins is a significant cause of food poisoning. Therefore, harvesting, cleansing, handling and heat treatment are covered by specific regulations in the food safety legislation.
Unless the mussels are to be eaten raw, the meats are normally removed by cooking the mussels in steam or boiling water.
The mussels should first be washed and then either steamed for about 4 minutes at 240°F (10 ½ lbs/square inch gauge pressure) or for about 6 minutes in boiling water at 212°F or steam at atmosphere pressure; some processors prefer boiling to steaming since the meats shrink less. Mussel meats immersed in boiling water are sterilized after about 2 ½ minutes; additional processing time should be just sufficient to cook the meats and no more, since overcooking causes excessive shrinkage of the meats. The liquor produced can be kept if required for use in bottling or canning. Cool the mussels quickly by water spray to prevent toughening of the meat.
The meats are removed from the now open shells, usually by hand, and the beard or byssus pulled out. One bushel of whole mussels should yield from 6 to 9 pounds of cooked meats. Percentage yield by weight may range from about 8 per cent to as high as 20 per cent of the whole mussels.
Wash the meats in clean fresh water, but do not leave them soaking in water or they will lose flavour and appear less attractive.
The meats are now ready either for marketing as they are, or for further processing - they can be frozen, smoked, bottled or canned. Each of these processes is described fully below.
There are no technical difficulties in preserving cooked mussel meats for long periods by freezing and cold storage; it is uneconomic to freeze the live mussel in shell.
The clean, cooked meats may be packed in a variety of containers before freezing, for example waxed cartons or polythene bags, or may be frozen unwrapped and packed or glazed afterwards.
Mussel meats lend themselves equally well to either the plate freezing or the air blast freezing process, since the meats are small and provide good surface contact with the cooling medium. An unwrapped block of meats an inch thick, frozen in a tray in an air blast freezer operating at - 20°F with an air speed of 1000 feet a minute, will take about 50 minutes to freeze to a temperature of - 5°F; a small waxed tub 3 inches tall, 2 inches in diameter and holding about 3oz. of meats might take up to 80 minutes under the same conditions.
Unwrapped meats should be glazed before storage, and all types of pack should preferably be stored at - 20°F; thawed meats after eight to nine months storage will then be in excellent condition with flavour and texture equal to fresh. Meats stored at - 7°F have been found to be of inferior quality after three months storage.
Thawing of the meats in 10° salt solution (4 1/2 oz. salt to a gallon of water), or soaking the thawed meats in a similar solution, may enhance the flavour, the salt acting as a condiment; the use of salt during cooking or subsequent rinsing of the meats before freezing may however accelerate the development of off flavours in the frozen meats during cold storage.
Mussels packed in glass are usually pickled either in brine or vinegar solution; they may or may not be heat processed.
The following method is a suitable one for bottling mussels in spiced vinegar:
The cooked, cleaned meats are brined for up to three hours in a 10° salt solution, drained and allowed to stand for three days in a vinegar and salt solution, made by mixing one part of distilled vinegar with two parts of water, and then adding up to 3 per cent of salt by weight. The solution may acquire a bluish tinge during this time, but this does not affect the flavour of the product.
The meats are then packed into glass jars and covered with spiced vinegar that has been diluted with an equal quantity of water. The jars are then sealed.
If the sealed jars are not processed, they should be kept cool (34° to 40°F) and not be exposed to strong light; they should then keep in good condition for 2 to 4 months.
If the meats are to be heat processed, a 5 oz. jar will require sterilization for about an hour at 212°F (atmospheric pressure) or 25-30 minutes at 221°F (3 lbs. gauge pressure). Shelf life should then be comparable with canned foods, but it is still necessary to avoid discoloration of the contents by protecting the jars from strong light.
Spiced vinegar may be made by adding the following spices to 5 pints of distilled vinegar mixed with 4 pints of water; 1/8 oz. bay leaves, 1/8 oz. white pepper, 1/4 oz. mustard seed, 1/8 oz. whole cloves, 1/8 oz. fennel 1/16 oz. paprika. The spices are simmered but not boiled in the vinegar for 45 minutes and then strained out; the solution is filtered and set aside to cool. The spice content may of course be varied to taste.
Mussel liquor obtained during extraction of the cooked meats from the shell may be used instead of water to dilute the solution before adding to the bottled meats.
Similarly white wine or wine vinegar may be used as alternatives to distilled vinegar.
Scrupulous care must be taken to ensure perfectly clean conditions throughout the bottling process.
Clean cooked meats are first pickled for three days in a vinegar solution made by adding one part of distilled vinegar to two parts of water. The jelly is prepared by dissolving ¼ lb gelatine in 4 pints of hot water to which has been added ¾ oz. of salt. When the jelly solution is cool, it is mixed with 2 pints of spiced vinegar and 2 pints of water. The meats are packed into jars and the mixture poured over them.
Jellied mussels are not processed and should be stored in a cool place; shelf life should be from 2 to 4 months.
The cooked, cleaned meats are first brined in a 50° brine for 5 minutes (made by adding 1 lb 8 ½ oz. of salt to each gallon of water).
The meats are then dipped in edible oil, spread out on wire mesh trays and smoked for 30 minutes in a dense smoke at 180°F; the temperature of the mechanical kiln should be raised to this temperature before the mussels are put in. Turn the meats over once during the process to ensure uniform smoking. In the Netherlands, the meats are sometimes dried for 25 minutes and then smoked for 25 minutes at 160°F.
The smoked meats are packed in small jars, covered with good quality edible oil and the jars sterilized at 250°F (15 lb per square inch gauge pressure). An 8 oz. jar requires about 15 minutes. The jars should be processed under water to prevent breakage, and cooled slowly. The smoked meats may also be packed in cans and heat processed.
Mussel meats may be canned in brine, or in a sauce, for example tomato sauce or tomato ketchup; smoked meats may be packed in brine or in edible oil.
The cooked, cleaned meats are washed in fresh water or in weak brine, but not soaked, and weighed into cans; washing in weak brine prevents loss of flavour where the meats are not to be canned in brine.
Boiling hot brine, made by dissolving 1 lb of salt in each gallon of water, is added to the can just before sealing; some head space is left, usually about ¼ inch for a can holding 5 to 6 oz. of meats.
This size of can requires about 25 minutes heat processing in a retort at 240°F (10 ½ lbs per square inch gauge pressure) or 30 minutes if the cans are loaded cold. Meats packed with sauce, or smoked meats in oil instead of brine, need sterilizing in a similar manner.
The meats shrink during processing; 6 lbs of meat may be reduced to 5 lbs drained weight after completion of the canning operation.
The liquor extracted during cooking of the meats may be used after clarification either as a substitute for the added brine in the can, or for making the brine; the liquor or bouillon adds a little to the food value of the contents, but makes no difference to the flavour of the meats.
Acetic acid is sometimes added to the brine before canning if the meats are infested with small pearls; this helps to dissolve the pearls during processing.
Cockles in Brine
Cockles in Vinegar
The cockle (Cardium edule) is a bivalve, usually white or cream in colour, with a roughly circular shell having ribs radiating from the hinge and is about one to one and a half inches in diameter when of marketable size. Though cockles are harvested throughout the year the meats are usually in best condition during the summer months and poorest from January to April.
The composition of cockle meat is similar to that of the mussel and contains about 81 per cent water and 19 per cent dry matter. Protein content is about 10 per cent, fat content about 1 per cent, depending on the season. Calorific value of the meat is about 86 calories per gramme wet weight.
Freshly gathered cockles will remain tightly closed or will close when touched and will not have any unpleasant smell.
After gathering, the cockles are usually washed in sea-water to remove surface mud or sand. Sometimes cockles contain a lot of sand or silt and they may be allowed to clean themselves by being placed in sea-water or fresh water to which salt has been added (3 ½ lbs salt to 10 gallons water), but in normal commercial processing washing after boiling is usually relied on to remove sand.
Cockles are as prone to sewage pollution and intoxication as mussels. They are usually only eaten cooked but controls on harvesting and marketing fall within the same regulatory regime as mussels.
After cooking, the meats are separated from the shells by shaking them, either by hand or mechanically, through a screen. The meats, which fall through, should then be transferred to several changes of clean fresh water for cooling and removal of debris. A final picking by hand may be necessary to remove any remaining pieces of shell.
The cockle meats may now be marketed fresh, frozen, or preserved in brine or in vinegar, or canned.
Cockle meats may be quick frozen and cold stored after cooking in a similar manner to that described for mussels.
Cockles are sometimes packed in bulk in brine for transport; a weak brine made with 1 lb of salt to 10 gallons of water is sufficient for shipment to local markets. A stronger brine must be used for conveyance to distant markets, and it is then usually necessary to reduce the salt content of the meats before sale by soaking them in fresh water.
Cockles may be bottled in brine:
Pack the meats into glass jars, and cover with 3° brine made from 1 Ib of salt to 10 gallons of water. Sterilize the contents by steaming the jars at 221 °F (3 lbs gauge pressure); a half pint jar will require about 35 minutes, a pint jar 50 minutes and a two-pint jar 70 minutes.
Cool the jars by gradually cooling the water in which they are immersed.
Soak the clean, cooked meats in 3° brine for about an hour; then drain and immerse the meats in a vinegar solution, made by mixing one part of distilled vinegar with two parts of water, to which has been added 3 per cent by weight of salt; leave them to stand for three days.
Drain the meats, pack them into glass jars and cover them with spiced vinegar diluted with an equal quantity of water. A recipe for spiced vinegar is given earlier under bottled mussels.
Without further processing, the pickled cockles will keep for two to four months provided that they are kept cool and protected from strong light.
The jars may be sterilized by heating them at 212°F for about an hour, or for about 30 minutes at 221 °F (3 lbs gauge pressure).
The cleaned, cooked meats are weighed into cans, hot 10° brine (made by adding 4 1/2 oz. salt to a gallon of water) is added, and the cans are exhausted and closed. The sealed cans are then heat processed, a time of about 30 minutes being necessary at 240°F (10 1/2 lbs gauge pressure) for cans with a capacity of about 6 oz.
The cooled and labelled cans may then be stored for indefinite periods, having a shelf life comparable with other canned foods.
Whelks in Vinegar
Whelks for Bait
The whelk (Buccinum undatum) is a univalve, gastropod mollusc. The shell is whorled or spiral-like, muddy yellow or brown in colour, and may be as long as three or four inches. Whelks are fished all the year round, but are at their best during the summer, from about April to August.
Whelks are caught mainly by baited iron-and-rope pots in coastal waters down to about 15 fathoms.
Whelks should be cooked soon after capture by boiling for 8 to 10 minutes for small, and 15 to 20 minutes for large ones at 212°F. Excessive boiling makes the meat very tough and less easily removed from the shell. The meats are removed from the shells by hand, and can be marketed fresh, frozen, pickled in vinegar, or canned.
The cooked meats can be quick frozen and cold stored as described for mussels; this often results in making the meat more tender.
Whelk meats have been smoked experimentally in a similar manner to mussels.
The process as described for mussels and cockles is also applicable to whelks.
Whelk meats have occasionally been canned, usually in brine in the same way as cockles.
Meats for bait can be more easily removed from the shell by first freezing and then thawing the whole whelks; the extracted meats can then be re-frozen if required for storage as bait.
If you have any queries, write, phone or call at either of the addresses given below:
The Officer in Charge
Torry Research Station
PO Box 31
135 Abbey Road
Tel: 0224 877071
Tel: 0482 27879
61 Gaping of fillets, by R. M. LOVE.
62 The freezing time of fish, by F. J. NICHOLSON.
63 Fishing ports in the UK, by J. J. WATERMAN.
64 Fish silage, by I. TATTERSON and M. L. WINDSOR.
65 Fishworking machinery, by S. MAIR.
66 Handling and processing mackerel, by J. N. KEAY.
67 The haddock, by J. J. WATERMAN.
68 Icemaking plant, by J. GRAHAM
69 Cook-freeze fish products, by J. N. KEAY.
70 Advice for the fish industry; who does what, by J. J. WATERMAN.
71 Processing cod; the influence of season and fishing ground, by R. M. LOVE.
72 Reducing odour in fish meal production.
73 Stowage of fish in chilled sea water, by J.H. KELMAN.
74 Handling and processing rainbow trout, by A. MILLS.
75 Freezing small pelagic fish, by I. MCDONALD.
76 Dark colour in white fish flesh, by R. M. LOVE.
77 Squid, by G. D. STROUD.
78 Health hazards of handling industrial fish, by A. WARD.
79 Minced fish by J. N. KEAY.
Earlier notes in the series, most of which are still available, are summarized in:
60 Key to Advisory Notes 1-59, by J. J. WATERMAN.
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