Learn About The Herring
Well I guess the U.N. actually has contributed something good to the world for once -- useful information about herring!!!!!
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Introduction
This note summarizes some useful background information about the herring for
those in the industry who want to know more about this important commercial
species.
Common, scientific and foreign names for herring are given, together with information on size, weight, life history and geographical distribution. The capture and landing of herring are briefly described, and there are notes on processing, distribution and marketing.
The name herring is used in other parts of the world to describe a number of species similar in appearance to the Atlantic herring.
Many local names have been applied in the past to herring, often to indicate size or condition, but most of these are now little used or obsolete. Examples are Dunbar wedder, nun, peeo, scadan, scattan, sgadan and sild. The names shaldoo, shaltoo, sile, yaulin’ and yawling have been used for small herring, and the names torn belly and wine drinker have been used to describe condition. In addition there are several names, originating from the old Crown Brand system of marking barrels of pickle cured herring, that are still occasionally used to describe the condition of the fish or the nature of the product made from them; these include filling, full, halflin, lafull, laspent, matfull, mattie, medium and spent.
The name Baltic herring is used to describe small Clupea harengus caught in that sea.
The herring has smooth gill covers, and moderately blunt keel scales along the edge of the belly, whereas the pilchard and the shads have radiating lines on the gill covers, and the sprat has pointed keel scales that feel prickly when a finger is run along the belly.
The body is covered with large, thin, loosely attached scales. The mouth is large, and contains small weak teeth. The lateral line is not visible, and there is no barbel.
The next graph shows the approximate relationship between the length of the
herring and the weight expressed as number of fish to the tonne. The range
between lean winter herring and fat summer herring is shown.
The eggs, which are about 1 mm in diameter, incubate for 10-30 days depending on sea temperature; 14-20 days is typical for the North Sea. The newly hatched fry, with yolk sacs attached, are 6-10 mm long and drift with the current. There they swim at first with small jerky movements and depend on nearby supplies of plankton for food.
When the larvae reach a length of about 40 mm, they begin to develop scales, take on a silvery sheen and move to inshore nursery grounds, where they are often caught together with the young of other fish, particularly sprats; the mixture of young herring and sprats is known as white-bait. North Sea herring leave the nurseries when about 2½ years old and move out to deep sea feeding grounds until they mature, mostly at 3 years of age.
The adult herring feeds mainly on animal plankton, particularly the tiny copepod called Calanus, near the surface of the sea. The gillrakers, a double row of slender bristles set into the inner edge of the gill arch, act as a sieve to strain out the food.
Maturing herring move in towards the spawning grounds as the milt and roe begin to develop, and congregate in huge shoals in coastal waters, where they swim close to the surface during darkness and deeper during daylight.
The migratory movements of the herring are not fully understood, but it has been established that on the east coast of Britain for example there is no great southward movement of the stocks between early summer off Shetland and the end of the year off East Anglia; although the fishery moves south, the herring taken are from quite different stocks, each with its own spawning time and place.
Nearly 90 per cent of the total catch came from waters adjacent to the coasts of Scotland and Northern Ireland.
The size of the British herring catch declined rapidly in the years after the Second World War until 1968, but since that date the amount caught has gradually increased. The following table shows the amount and value of the catch in recent years.
Quantity and value of herring caught by British vessels
The principal ports for herring, at which more than 5,000 tonnes were landed in 1970 are listed bellow.
More detailed figures for the quantity and value of herring landed in Britain are given in the Sea Fisheries Statistical Tables and the Scottish Sea Fisheries Statistical Tables published annually by HM Stationery Office for the Ministry of Agriculture, Fisheries and Food and the Department of Agriculture and Fisheries for Scotland respectively, and also in the annual reports of the Herring Industry Board.
Conservation measures are introduced from time to time to protect the herring stocks; for example, on the recommendations of the North East Atlantic Fisheries Commission the catching of herring in certain sea areas may be prohibited at certain times of the year, and the use of some types of fishing gear may be prohibited in specific areas, as for example the current ban on use of the purse seine in certain parts of the southern Irish Sea.
The herring is a highly perishable fish; careful handling and rapid cooling are essential for herring destined for the human food market.
Herring are not normally gutted at sea, because it is impracticable to handle the large numbers of small fish coming aboard in a short time; chilling or freezing soon after capture is therefore all the more important to prevent spoilage.
The traditional method of chilling on board the fishing vessel was in ice. The herring should be stowed in boxes with a layer of ice above and below the fish and some ice sprinkled among the fish; with top icing only, the layer of fish in a typical box 20 cm deep is too thick to be effectively cooled in the short time available. The ratio of ice to fish should approach 1:3 in the summer. During heavy fishing, herring are sometimes stowed in bulk in the fishroom, with or without ice. It is difficult to ice the catch adequately in bulk, and some of the fish will be damaged in deep stowage; uniced fish in bulk are generally suitable only for reduction to meal and oil.
An alternative method of chilling is stowage in fixed tanks filled with refrigerated sea water. A possible development of this method is the use of portable tanks containing ice and sea water that can be filled in the fish-room with herring and transferred to lorry at the quayside for onward conveyance to the processing factory. The freezer trawler can be used for catching and freezing herring at sea; small quantities have been handled in this way in the British fishery, and the use of shipborne vertical plate freezers for the production of blocks of sea frozen herring is likely to increase; the product, frozen immediately after capture, is of high quality and can be stored ashore at -30°C for long periods without appreciable change in quality.
The keeping times for herring stowed unchilled, chilled or frozen are as follows. Ungutted herring of medium fat content will keep in good condition for about 10 hours at 15°C, and will be spoilt in about 30 hours. Properly stowed in plenty of ice, or immersed in refrigerated sea water, herring will keep in good condition for 2-3 days and will become unacceptable after 5-6 days. Precise keeping times will depend on the fat content of the herring and the amount of food in the gut; herring with a fat content of 20 per cent or more will keep for a shorter time than the figures given, while herring with a low fat content of 5 per cent or less may keep for a little longer. Herring frozen at sea immediately after capture will keep in good condition for 7 months at -30°C.
Handling on shore
Boxed iced herring are moved mostly by road from the landing ports to the factories; since a great deal of the catch is landed at ports on the west coast of Scotland that have few processing facilities, long lorry journeys are often made to factories in the north east of Scotland and in the Humber area. Since the land journey is an extension of the period of chilled storage, the herring should remain well iced; the ratio of ice to fish should be about 1:3 for long hauls in warm weather, particularly when the lorry is uninsulated.
Some herring is sold to foreign buyers and conveyed by road to the Continent; a mixture of ice and salt is sometimes used on the fish to lower the temperature and thus reduce spoilage during the long journey; this treatment is known as klondyking, and the same method is also used for transshipments consigned by sea on carrier vessels to the Continent. Because klondyked herring are usually destined for Continental buyers, the term klondyking is now sometimes used incorrectly to mean any export of chilled herring, whether salt has been added to the ice or not, or the export of semipreserves of herring in sugar and spice.
Freezing and cold storage
Whole ungutted herring, frozen within a few hours of capture and properly cold stored at -30°C, can be kept 7 months before thawing to make good quality smoked, canned or marinated products. Ideally the herring should be frozen not later than 24 hours or, when the fat content is high, 18 hours after capture, and the herring should be kept properly chilled between catching and freezing.
Whole herring can be frozen in either air blast or vertical plate freezers. For blast freezing, the herring are usually laid in single layers on trays, with the heads to the end of the block; typical freezing time in air at -35°C moving at 3 m/s is about 90 minutes. The frozen blocks are removed from the trays, glazed by spraying or dipping, and packed in outer fibreboard cartons for storage. Herring can be frozen satisfactorily in vertical plate freezers in blocks 50-100 mm thick; in one method an open polythene bag is placed between the plates, herring are poured into the bag, and the voids in the block filled with water. Freezing times for a 50 mm block and a 100 mm block are 2 hours and 4 hours respectively with refrigerant at -35°C. Blocks encased in ice and wrapped in this way are well protected against dehydration, oxidation and physical damage. The frozen blocks may require additional packaging, in fibreboard for example, where the slippery polythene bags make handling dangerous.
Herring can also be frozen after splitting or filleting if required; they are most conveniently frozen in blocks in a horizontal plate freezer. The herring should be packed in layers in moulds or trays with cut surfaces together and skins to the outside of the block. Since storage life will be reduced if cut surfaces are exposed to air, the frozen blocks should be glazed before storage, and preferably packed in polythene bags to reduce the onset of rancidity.
Blocks of frozen whole herring can be thawed before processing in warm air or warm water, or by vapour phase thawing. Thawing methods are described in Advisory Note 25.
Smoking
The kipper and the kipper fillet are the most important smoked products made from herring in Britain. Kippers are made by cold smoking fat herring that have been gutted, split down the back, lightly brined and dyed if required. The smoking temperature does not exceed 30°C and the smoking process takes about 4 hours in a mechanical kiln to give a weight loss of about 14 per cent. The manufacture of kippers is described in detail in Advisory Note 48.
Other smoked herring products made in small quantities in Britain include the bloater, the buckling and the red herring. Bloaters are whole ungutted herring, dry salted for about 6 hours and cold smoked for 8-12 hours in a traditional chimney kiln or 4 hours in a mechanical kiln; the fish are dried without smoke for most of the time in the kiln, and smoke is applied only during the last hour or so, so that the fish retain their bright silver appearance. Buckling are hot smoked herring; the flesh is cooked during the smoking process. In British practice the herring are nobbed, that is the head and long gut are removed, brined, and smoked for about 3 hours in a mechanical kiln, the temperature being raised gradually from about 30°C at the start to 75°C during the last hour. Red herring are whole ungutted herring that have been heavily salted and then cold smoked for 2-3 weeks; the hard cured product is exported, mainly to Mediterranean countries.
Canning
Herring in tomato sauce is the principal canned fish product in Britain; the cans are packed with nobbed, brined herring, filled with tomato sauce, closed and heat processed. Smoked herring products, particularly kippers and kipper fillets, are also canned in Britain.
Salting
Apart from the salting of herring as a preliminary step in the manufacture of products like kippers and red herring, a small proportion of the British herring catch, about 2 per cent, is still preserved in salt by pickle curing, that is packing in barrels with salt so that the fish are pickled in the liquid that is formed. Pickle cured herring are mainly exported to the Continent. A typical barrel has a capacity of about 120 litres, and holds about 120 kg of Scotch cured herring and 25 kg of pickle.
Marinating
About 2 per cent of the British herring catch is marinated, that is preserved in a mixture of acetic acid and salt; fillets of herring treated in this way to make a number of products like rollmops and Bismarck herring have a limited shelf life; the products are known as semipreserves. The marinating process is described in detail in Advisory Note 56.
Animal food
Herring of a size or quality unsuitable for processing as human food are used in the manufacture of animal food. Some are used as raw material for canned petfood, and some, together with herring processing waste, are cooked, pressed to extract the oil, dried and ground to make fish meal, a valuable protein constituent of pig and poultry food. The extracted herring oil is refined and, when hydrogenated, is used to a large extent in margarine manufacture. The fish meal process is described in Advisory Note 49.
Using the following graphs, it is possible to estimate the fat and protein content with reasonable accuracy when the water content is known.
The herring as a food has a high energy value because most of the fat is in
the flesh; the raw flesh of a moderately fat herring, containing 11 per cent
fat, has an energy value of about 7·4 kJ/g.
The approximate amounts of vitamins A, B and D in herring flesh are as follows.
Vitamins in herring flesh mg/kg
Herring also contain appreciable amounts of iron, calcium and iodine.
Yields
Thanks to Uncle Sammy for finding this one!
Common, scientific and foreign names for herring are given, together with information on size, weight, life history and geographical distribution. The capture and landing of herring are briefly described, and there are notes on processing, distribution and marketing.
Scientific names
The scientific name for the herring found in the north Atlantic is Clupea harengus. The scientific name for the Pacific herring, a closely related species, is Clupea pallasii.Common names
The name herring is used officially in Britain to describe only the one species, and there are no other common names in general use. The name Atlantic herring is used when it is necessary to distinguish it from the Pacific herring. The name sea herring is sometimes applied to Clupea harengus on the Atlantic coast of the USA to distinguish it from the shads, Alosa species.The name herring is used in other parts of the world to describe a number of species similar in appearance to the Atlantic herring.
Many local names have been applied in the past to herring, often to indicate size or condition, but most of these are now little used or obsolete. Examples are Dunbar wedder, nun, peeo, scadan, scattan, sgadan and sild. The names shaldoo, shaltoo, sile, yaulin’ and yawling have been used for small herring, and the names torn belly and wine drinker have been used to describe condition. In addition there are several names, originating from the old Crown Brand system of marking barrels of pickle cured herring, that are still occasionally used to describe the condition of the fish or the nature of the product made from them; these include filling, full, halflin, lafull, laspent, matfull, mattie, medium and spent.
The name Baltic herring is used to describe small Clupea harengus caught in that sea.
Foreign names
| Danish | sild | Norwegian | sild |
| Dutch | baring | Polish | sledz |
| Finnish | silli, silakka | Portuguese | arenque |
| French | hareng | Russian | seld |
| German | hering | Spanish | arenque |
| Greek | régha | Swedish | sill |
| Icelandic | sild | Turkish | ringa |
| Italian | aringa | Yugoslavian | heringa, sledy |
| Japanese | nishin, kadoiwashi |
|
|
Distinguishing features
The body of the herring is deeper than it is thick, and the length of the fish is about five times the greatest depth. The upper part of the body is dark blue green, or steel blue, and the snout is blackish blue; the sides and belly are silvery. The lower jaw protrudes slightly beyond the upper. There is a single short back fin, a short anal fin near the tail, and a deeply forked tail fin. The pelvic fins are behind the start of the back fin, whereas on the sprat they are in front.The herring has smooth gill covers, and moderately blunt keel scales along the edge of the belly, whereas the pilchard and the shads have radiating lines on the gill covers, and the sprat has pointed keel scales that feel prickly when a finger is run along the belly.
The body is covered with large, thin, loosely attached scales. The mouth is large, and contains small weak teeth. The lateral line is not visible, and there is no barbel.
Size
Most of the herring landed in Britain are between 23 and 30 cm long; herring caught off Norway and Iceland are often larger, up to 36 cm. Occasionally a herring reaches a length of about 43 cm, but this is exceptional.Weight
The weight of a herring in relation to its length is shown in the following graph. The weight for a given length can vary considerably from season to season and from year to year; the range commonly encountered is shown. The weights are for ungutted fish.
Fig. 2 Length and weight of ungutted herring.
Geographical distribution
The herring is found on both sides of the north Atlantic. In the north east Atlantic it occurs from the Bay of Biscay in the south to Spitzbergen and Novaya Zemlya in the north, while in the north west Atlantic it occurs from the coast of Maine northwards. The most important fishing grounds are the North Sea, the Baltic Sea, and the coastal waters of Britain, Norway, Iceland and Canada.
Fig. 3 Number of herring to the tonne.
Life history
The herring is a pelagic fish, and may be found anywhere between 2 and 400 m below the surface of the sea. The female herring lays its eggs on the sea bed, usually in water 10-80 m deep, on hard ground covered with small stones, shells or seaweed to which the naturally sticky eggs can attach themselves. One female may lay 20,000-40,000 eggs. The eggs are fertilized in the water by the male herrings, which discharge their sperms at the same time as the females lay their eggs.The eggs, which are about 1 mm in diameter, incubate for 10-30 days depending on sea temperature; 14-20 days is typical for the North Sea. The newly hatched fry, with yolk sacs attached, are 6-10 mm long and drift with the current. There they swim at first with small jerky movements and depend on nearby supplies of plankton for food.
When the larvae reach a length of about 40 mm, they begin to develop scales, take on a silvery sheen and move to inshore nursery grounds, where they are often caught together with the young of other fish, particularly sprats; the mixture of young herring and sprats is known as white-bait. North Sea herring leave the nurseries when about 2½ years old and move out to deep sea feeding grounds until they mature, mostly at 3 years of age.
The adult herring feeds mainly on animal plankton, particularly the tiny copepod called Calanus, near the surface of the sea. The gillrakers, a double row of slender bristles set into the inner edge of the gill arch, act as a sieve to strain out the food.
Maturing herring move in towards the spawning grounds as the milt and roe begin to develop, and congregate in huge shoals in coastal waters, where they swim close to the surface during darkness and deeper during daylight.
The migratory movements of the herring are not fully understood, but it has been established that on the east coast of Britain for example there is no great southward movement of the stocks between early summer off Shetland and the end of the year off East Anglia; although the fishery moves south, the herring taken are from quite different stocks, each with its own spawning time and place.
The fishery
The herring fishery is, and always has been, unpredictable. Nevertheless each ground around the British coast has its season, and the fishery at any one place is rarely exploited outside these periods. During a season the size of catch can fluctuate enormously from year to year and, in some instances, as off East Anglia for example, the stocks may disappear completely, perhaps for several years.| fishing ground | herring season |
| Shetland | May to September |
| Peterhead | May to August |
| Yorkshire | August to October |
| East Anglia | October to December |
| Milford Haven | December to February |
| Isle of Man | June to October |
| Clyde | all year round |
| Minches | May to March |
Nearly 90 per cent of the total catch came from waters adjacent to the coasts of Scotland and Northern Ireland.
The size of the British herring catch declined rapidly in the years after the Second World War until 1968, but since that date the amount caught has gradually increased. The following table shows the amount and value of the catch in recent years.
Quantity and value of herring caught by British vessels
|
year
|
thousand tonnes
|
£ million
|
|
1938
|
276
|
1·9
|
|
1948
|
270
|
5·4
|
|
1951
|
169
|
3·7
|
|
1960
|
111
|
2·5
|
|
1966
|
115
|
2·9
|
|
1967
|
102
|
2·7
|
|
1968
|
95
|
2·6
|
|
1969
|
124
|
3·3
|
|
1970
|
145
|
4·7
|
The principal ports for herring, at which more than 5,000 tonnes were landed in 1970 are listed bellow.
More detailed figures for the quantity and value of herring landed in Britain are given in the Sea Fisheries Statistical Tables and the Scottish Sea Fisheries Statistical Tables published annually by HM Stationery Office for the Ministry of Agriculture, Fisheries and Food and the Department of Agriculture and Fisheries for Scotland respectively, and also in the annual reports of the Herring Industry Board.
Conservation measures are introduced from time to time to protect the herring stocks; for example, on the recommendations of the North East Atlantic Fisheries Commission the catching of herring in certain sea areas may be prohibited at certain times of the year, and the use of some types of fishing gear may be prohibited in specific areas, as for example the current ban on use of the purse seine in certain parts of the southern Irish Sea.
|
Port
|
quantity landed tonnes
|
% British herring catch
|
| Mallaig |
35,400
|
24·5
|
| Ullapool |
27,400
|
18·9
|
| Lerwick & Bressay |
12,400
|
8·5
|
| Oban |
10,000
|
6·9
|
| Stornoway |
8,200
|
5·6
|
| Uig |
7,600
|
5·2
|
| Fraserburgh |
6,600
|
4·5
|
| Ayr |
6,100
|
4·2
|
|
|
113,700
|
78·3
|
| 1970 total |
145,000 tonnes
|
100·0%
|
Handling and transporting herring
Handling at seaThe herring is a highly perishable fish; careful handling and rapid cooling are essential for herring destined for the human food market.
Herring are not normally gutted at sea, because it is impracticable to handle the large numbers of small fish coming aboard in a short time; chilling or freezing soon after capture is therefore all the more important to prevent spoilage.
The traditional method of chilling on board the fishing vessel was in ice. The herring should be stowed in boxes with a layer of ice above and below the fish and some ice sprinkled among the fish; with top icing only, the layer of fish in a typical box 20 cm deep is too thick to be effectively cooled in the short time available. The ratio of ice to fish should approach 1:3 in the summer. During heavy fishing, herring are sometimes stowed in bulk in the fishroom, with or without ice. It is difficult to ice the catch adequately in bulk, and some of the fish will be damaged in deep stowage; uniced fish in bulk are generally suitable only for reduction to meal and oil.
An alternative method of chilling is stowage in fixed tanks filled with refrigerated sea water. A possible development of this method is the use of portable tanks containing ice and sea water that can be filled in the fish-room with herring and transferred to lorry at the quayside for onward conveyance to the processing factory. The freezer trawler can be used for catching and freezing herring at sea; small quantities have been handled in this way in the British fishery, and the use of shipborne vertical plate freezers for the production of blocks of sea frozen herring is likely to increase; the product, frozen immediately after capture, is of high quality and can be stored ashore at -30°C for long periods without appreciable change in quality.
The keeping times for herring stowed unchilled, chilled or frozen are as follows. Ungutted herring of medium fat content will keep in good condition for about 10 hours at 15°C, and will be spoilt in about 30 hours. Properly stowed in plenty of ice, or immersed in refrigerated sea water, herring will keep in good condition for 2-3 days and will become unacceptable after 5-6 days. Precise keeping times will depend on the fat content of the herring and the amount of food in the gut; herring with a fat content of 20 per cent or more will keep for a shorter time than the figures given, while herring with a low fat content of 5 per cent or less may keep for a little longer. Herring frozen at sea immediately after capture will keep in good condition for 7 months at -30°C.
Handling on shore
Boxed iced herring are moved mostly by road from the landing ports to the factories; since a great deal of the catch is landed at ports on the west coast of Scotland that have few processing facilities, long lorry journeys are often made to factories in the north east of Scotland and in the Humber area. Since the land journey is an extension of the period of chilled storage, the herring should remain well iced; the ratio of ice to fish should be about 1:3 for long hauls in warm weather, particularly when the lorry is uninsulated.
Some herring is sold to foreign buyers and conveyed by road to the Continent; a mixture of ice and salt is sometimes used on the fish to lower the temperature and thus reduce spoilage during the long journey; this treatment is known as klondyking, and the same method is also used for transshipments consigned by sea on carrier vessels to the Continent. Because klondyked herring are usually destined for Continental buyers, the term klondyking is now sometimes used incorrectly to mean any export of chilled herring, whether salt has been added to the ice or not, or the export of semipreserves of herring in sugar and spice.
Herring processing
Although some herring is distributed and sold unprocessed, either whole or as boned herring, most of the catch is processed in some way before sale. The main food outlets are for smoked, salted, marinated and canned products; quick freezing and cold storage are used as a means of preserving some of the catch prior to making these products, and for preserving some of the finished products.Freezing and cold storage
Whole ungutted herring, frozen within a few hours of capture and properly cold stored at -30°C, can be kept 7 months before thawing to make good quality smoked, canned or marinated products. Ideally the herring should be frozen not later than 24 hours or, when the fat content is high, 18 hours after capture, and the herring should be kept properly chilled between catching and freezing.
Whole herring can be frozen in either air blast or vertical plate freezers. For blast freezing, the herring are usually laid in single layers on trays, with the heads to the end of the block; typical freezing time in air at -35°C moving at 3 m/s is about 90 minutes. The frozen blocks are removed from the trays, glazed by spraying or dipping, and packed in outer fibreboard cartons for storage. Herring can be frozen satisfactorily in vertical plate freezers in blocks 50-100 mm thick; in one method an open polythene bag is placed between the plates, herring are poured into the bag, and the voids in the block filled with water. Freezing times for a 50 mm block and a 100 mm block are 2 hours and 4 hours respectively with refrigerant at -35°C. Blocks encased in ice and wrapped in this way are well protected against dehydration, oxidation and physical damage. The frozen blocks may require additional packaging, in fibreboard for example, where the slippery polythene bags make handling dangerous.
Herring can also be frozen after splitting or filleting if required; they are most conveniently frozen in blocks in a horizontal plate freezer. The herring should be packed in layers in moulds or trays with cut surfaces together and skins to the outside of the block. Since storage life will be reduced if cut surfaces are exposed to air, the frozen blocks should be glazed before storage, and preferably packed in polythene bags to reduce the onset of rancidity.
Blocks of frozen whole herring can be thawed before processing in warm air or warm water, or by vapour phase thawing. Thawing methods are described in Advisory Note 25.
Smoking
The kipper and the kipper fillet are the most important smoked products made from herring in Britain. Kippers are made by cold smoking fat herring that have been gutted, split down the back, lightly brined and dyed if required. The smoking temperature does not exceed 30°C and the smoking process takes about 4 hours in a mechanical kiln to give a weight loss of about 14 per cent. The manufacture of kippers is described in detail in Advisory Note 48.
Other smoked herring products made in small quantities in Britain include the bloater, the buckling and the red herring. Bloaters are whole ungutted herring, dry salted for about 6 hours and cold smoked for 8-12 hours in a traditional chimney kiln or 4 hours in a mechanical kiln; the fish are dried without smoke for most of the time in the kiln, and smoke is applied only during the last hour or so, so that the fish retain their bright silver appearance. Buckling are hot smoked herring; the flesh is cooked during the smoking process. In British practice the herring are nobbed, that is the head and long gut are removed, brined, and smoked for about 3 hours in a mechanical kiln, the temperature being raised gradually from about 30°C at the start to 75°C during the last hour. Red herring are whole ungutted herring that have been heavily salted and then cold smoked for 2-3 weeks; the hard cured product is exported, mainly to Mediterranean countries.
Canning
Herring in tomato sauce is the principal canned fish product in Britain; the cans are packed with nobbed, brined herring, filled with tomato sauce, closed and heat processed. Smoked herring products, particularly kippers and kipper fillets, are also canned in Britain.
Salting
Apart from the salting of herring as a preliminary step in the manufacture of products like kippers and red herring, a small proportion of the British herring catch, about 2 per cent, is still preserved in salt by pickle curing, that is packing in barrels with salt so that the fish are pickled in the liquid that is formed. Pickle cured herring are mainly exported to the Continent. A typical barrel has a capacity of about 120 litres, and holds about 120 kg of Scotch cured herring and 25 kg of pickle.
Marinating
About 2 per cent of the British herring catch is marinated, that is preserved in a mixture of acetic acid and salt; fillets of herring treated in this way to make a number of products like rollmops and Bismarck herring have a limited shelf life; the products are known as semipreserves. The marinating process is described in detail in Advisory Note 56.
Animal food
Herring of a size or quality unsuitable for processing as human food are used in the manufacture of animal food. Some are used as raw material for canned petfood, and some, together with herring processing waste, are cooked, pressed to extract the oil, dried and ground to make fish meal, a valuable protein constituent of pig and poultry food. The extracted herring oil is refined and, when hydrogenated, is used to a large extent in margarine manufacture. The fish meal process is described in Advisory Note 49.
Chemical composition
Unlike most white fish, the chemical composition of herring varies considerably with the season and the breeding cycle; the fat content of herring may be less than 1 per cent immediately after spawning, and more than 20 per cent as spawning time approaches again. The water content decreases as the fat content increases. In addition the protein content varies with water content; as the water content increases, so the protein content rises a little. The range of water, fat and protein content encountered in British-caught herring is shown below.|
|
water %
|
fat %
|
protein %
|
| whole herring |
60-80
|
0·4-22
|
16-19
|
| herring flesh |
57-79
|
0·8-24·9
|
14-17
|
Using the following graphs, it is possible to estimate the fat and protein content with reasonable accuracy when the water content is known.
Fig. 4 Fat content of herring.
Fig. 5 Protein content of herring.
The approximate amounts of vitamins A, B and D in herring flesh are as follows.
Vitamins in herring flesh mg/kg
| A | D |
B vitamins
| ||||||
|
|
|
thiamine
|
riboflavin
|
niacin
|
B6
|
B12
|
pantothenic acid
|
biotin
|
|
6-120
|
7-25
|
0.1-1.3
|
0.9-3.3
|
20-63
|
3.5-4.2
|
0.08-0.14
|
9.3-9.7
|
0.09-0.16
|
Herring also contain appreciable amounts of iron, calcium and iodine.
Stowage rates and yields
Stowage rates|
method of stowage
|
density kg/m3
|
space occupied m³/tonne
| |
| whole herring |
|
| |
|
|
in bulk uniced |
930
|
1·1
|
| in rsw |
770
|
1·3
| |
| boxed in ice |
650
|
1·5
| |
| frozen in blocks |
850
|
1·2
| |
| kippers |
|
| |
|
|
in 1-stone wooden boxes (6·3 kg) |
500
|
2·0
|
Yields
|
product
|
multiply ungutted landed weight by
|
| fillets with skin | 0·53 |
| range 0·47-0·58 depending on condition | |
| kippers | 0·65-0·70 |
| bloaters | 0·68-0·80 |
| red herring | 0·60-0·62 |
|
pickle cured (net content of barrel) |
0·79-0·88 |
Thanks to Uncle Sammy for finding this one!
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