Table of Contents


Introduction
The fishery
Handling the catch
Boiling
Composition of cooked flesh
Assessment of quality
Extracting the meats
Freezing unshelled tails
Freezing shelled meats
A summary guide to good processing

Introduction

The species referred to in this Note is the Norway lobster, whose scientific name is Nephrops norvegicus. It is also known as the Dublin Bay prawn or, more simply but less correctly, as the prawn. Norway lobsters and particularly the shelled tail meats have also become known in this country in recent years by the name scampi, which is the plural of the Italian word scampo, meaning Norway lobster.

The Norway lobster has five pairs of articulated limbs, the foremost pair being long, slender claws about equal in length to the body. There are two pairs of feelers on the head, one a very long pair with a pair of short, split ones between them. The eyes are large and black. The abdomen, or tail, has seven segments including the fan-like tail piece.

This Note describes the handling, chilling and freezing of the tails, and extraction and freezing of the meats. Brief reference is also made to cooking and to composition of the cooked meat.

The fishery

The Norway lobster is found in the North Sea, the north-east Atlantic and the Mediterranean, and is fished commercially from north Africa to north Norway and Iceland; France, Britain, Denmark and Italy are the principal catching countries.

The Norway lobster lives on a muddy sea bottom and occurs around most of the British coast, mainly in depths from 10 fathoms down to 120 fathoms or more. Catches have increased tremendously in the last decade to meet rising demands, and in 1964 it was the most valuable crustacean sold in Scotland, where over 90 per cent of the British catch is landed. Principal British grounds are off the east and west coasts of Scotland and northern England, and in the Irish Sea; landings take place at all seasons, but catches are highest in summer, reaching a peak about July.

The adult Norway lobster burrows in the mud and eats almost any flesh available, including worms, fish and shellfish. The female becomes mature when about 3¼ inches long and spawns annually, carrying eggs under her tail from early autumn until late the following spring when they hatch into minute larvae.

Most Norway lobsters are captured by means of a specially designed light trawl, while others are captured incidentally during trawling and seining for white fish; a few are caught occasionally in baited pots. There is some evidence to suggest that catches in the trawl are largest at dawn and dusk each day.

Handling the catch

Norway lobsters are either landed whole, in which case they should be still alive, or the head and carapace, with claws and legs attached, should be twisted off and discarded at sea, leaving only the unshelled tails to be landed. It is preferable to land them in this way because the digestive gland in the dead whole fish rapidly breaks down and digests the edible flesh, causing discolouration and off flavours. Also the amount of meat in the claws is small and is rarely extracted. The severed tails should be washed and then stowed in plenty of ice right away. Where the tails are separated ashore, they should also be washed and packed with ice in boxes for onward transmission to the factory.

Large tails in prime condition may average as few as 8-10 to the pound; rough categories by weight of unshelled tail are: large, less than 16 to the pound; medium, about 30; small, about 50 to the pound. Large shelled tail meats average less than 26 to the pound; medium, 26-65; small, more than 65 to the pound.

The greater part of the British catch is sold as frozen, uncooked, shelled meats; unshelled tails are also sold fresh, usually uncooked but occasionally cooked. Small quantities of the shelled meats are also sold cooked. The Norway lobster is very rarely sold whole to the consumer in this country, whereas on the Continent they are almost always sold whole, either raw or cooked.

Boiling

Whole Norway lobsters or unshelled tails should be boiled in water containing about 5 per cent salt, that is about 8 oz of salt to a gallon of water. The lobsters should be put into boiling water and cooked for about 5-6 minutes; shelled meats require from 3-5 minutes, depending on size.

Composition of cooked flesh

Boiled Norway lobster meats contain about 72-75 per cent water, 21-24 per cent protein, about 3 per cent minerals and 1-2 per cent salt depending on the brine strength used for cooking.

Assessment of quality

The following brief descriptions of appearance, odour and taste give a rough measure of the freshness of Norway lobsters:



Fresh

Spoiling

Spoiled

Raw appearance:

shell

pale pink or rose to orange-red

lighter and greyish

greyish green to black with brownish spots


gills

rose to pale grey

grey more marked

dark grey, brown to black


meat

firm, opaque, no fluid from claw when broken open

less firm, translucent, increased fluid from claw

very soft, discoloured


blood-vessel

bright red


brown

Raw odour:


characteristic mild shellfishy

stronger and sharper

objectionable fetid

Cooked:

meat

in one piece; opalescent white to very faint pink on the surface; firm, chewy and sweet

tends to break up, fibres easily separated, pink; tasteless

broken up, mushy pink with black patches; foamy material between shell and meat; unpleasant sour or bitter taste

Extracting the meats

The raw flesh in the tail of the freshly caught Norway lobster is held to the shell by a membrane, making it difficult to remove the meat. If the tails are kept in ice for periods up to 72 hours or more, depending on their seasonal condition, the membrane breaks down and the flesh is easily taken out; many processors therefore deliberately store the tails in ice until this process of digestion of the membrane is completed. Unfortunately self digestion is not confined to the membrane; both the flesh and the gut, or weed, are also affected. During this process pink pigment is released from cells in the membrane and the flesh acquires a characteristic pink colour on the surface; unfortunately, the gut disintegrates, contaminating the flesh with its contents, and the removal of the pieces is a laborious task normally carried out by using tweezers. The flesh also loses some of its initial sweetness and sometimes objectionable odours and flavours may develop. Yield of meat too is often reduced due to self digestion of the flesh.

Most of the drawbacks associated with prolonged iced storage can be completely avoided by freezing the fresh whole tails, both as a means towards releasing the meats, and as a way of storing the raw material from times of glut to times of scarcity. The advantages of freezing unshelled tails are fully discussed in the next section.

As soon as the flesh can be separated from the shell, the meats are removed by hand, or by blowing out the contents with compressed air jets. The meats are picked clean and all traces of gut removed, then washed and graded. A candling table is sometimes used to inspect the meats to make sure no gut or gut contents remain; the meats are sometimes laid out on white, translucent plastic or glass fibre trays to make inspection easier.

Freezing unshelled tails

Provided the unshelled tails are very fresh, it is perfectly feasible to freeze and store them for processing later and there are several advantages in doing this.

The supply of tails fluctuates from day to day and month to month. Supplies for processing throughout the year are thus regulated by freezing the whole tails very soon after catching and building up reserve stocks in cold storage.

The meats are much more easily and neatly removed from the frozen tails after thawing than from tails that have been kept in ice for several days; the yield is greater and quality is markedly better. The gut normally remains intact and is often removed with the shell; tedious and costly hand picking is largely eliminated. The links between the articulated segments of the tail shell retain their strength when frozen, so that the tail shell structure remains intact after thawing; this in turn means that air jets can be used successfully to blow out the meats; gaps between shell segments on a partly spoiled iced tail often make this method of extraction ineffective.

Thawed frozen tails are of uniformly good quality and present no problems on the production line, whereas chilled tails often remain in ice much longer than is necessary; five or six days in the chill room is quite common in practice. This happens because it is often impossible to judge how much material needs to be iced down at any one time to maintain steady production, since the time needed for the membrane between flesh and shell to break down can vary a great deal, depending on the condition of the Norway lobsters when caught, and on handling prior to processing.

Because the meats can be extracted cleanly in one piece, yield from frozen tails is at least 3 per cent higher than from iced tails, and may be as much as 5 per cent more. In addition none are discarded due to spoilage prior to shelling.

Thawed tails yield meats with a sweet shellfish taste and firm texture, but iced tails, even when handled as expeditiously as possible, lose some of their flavour and, when left overlong in ice, are often tasteless or even sour or bitter.

Since spoilage is arrested by the freezing process, the marked pink discoloration that appears in iced tail meats is absent in thawed frozen ones; the surface of the flesh remains white or only very slightly pink. Absence of pink colouring should not be regarded as a disadvantage of freezing or as a reason for rejecting the product; white meats are fresh meats, pink ones are staler.

Provided that freezing is carried out within 36 hours of death, and that the tails have been kept in ample ice until they are frozen, the thawed tails will yield meats of first class quality. The tails can be frozen singly in an air blast freezer, or as blocks bound together with water in a horizontal plate freezer. Plate freezing of blocks is probably easier in a small factory, but in larger plants individual blast-frozen tails can be stored in bulk in containers on pallets and quickly thawed when required.

The frozen tails should be wrapped in a vapour-tight material, such as a suitable plastic film, to prevent drying of the product in cold storage. The wrapped tails should be stored at a temperature of minus 20 °F for safe keeping; under these conditions they can be held for up to 6 months without significant change in quality.

The single tails and blocks can be thawed when required either in moist air or in tap water not warmer than 65°F. Single tails will thaw in water at mains temperature in about 30 minutes; 3-lb blocks will take about an hour. Too long a soaking after they are thawed results in some loss of flavour.

Freezing shelled meats

The cleaned meats can be frozen either singly or in blocks in an air blast or plate freezer respectively in just the same manner as the unshelled tails. The meats should then be glazed, wrapped and stored at minus 20°F, for safe keeping for at least 2 or 3 months.

A summary guide to good processing

1. The raw material must be as fresh as possible. For best results, the tails should be frozen within 36 hours of death.

2. Tails should be stowed in ice as soon as they are separated from the rest of the body, whether this takes place on board or on shore, and remain well iced until they reach the processor.

3. Tails more than 36 hours old on arrival at a processor’s premises should be marked so that they will not be frozen and cold stored before shelling and processing.

4. All very fresh tails should be frozen to keep them fresh and to release the meats.

5. Glaze and wrap the frozen tails and store them at minus 20°F; they will be safe for 6 months.

6. Thaw the tails, in the same order as they were frozen, when they are needed for production; use moist air or tap water, and don’t soak them too long.

7. Shell and clean the tails within 2-3 hours of thawing; if a longer delay is unavoidable, then ice them thoroughly while they are waiting.

8. Blow out the meats with compressed air, clean off the few remaining traces of gut, and wash them.

9. Inspect the meats for defects.

10. Re-freeze the shelled meats, glaze and wrap them, and store at minus 20°F until distributed.


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