Freezing and cold storage of roes
Smoked cod roes
Salted cod roes
Canned cod roes
Cod roe sausage
The cod (Gadus morhua) spawns in the north-east Atlantic during the first three or four months of the year, and British fishing vessels make their heaviest landings of roes from about January to April.
The roes, which may constitute as much as 10% or more of the weight of ripe female cod, are collected when the fish are gutted at sea and are either packed in small sacks and held in chilled storage on ice in the fishroom, or, on trawlers fitted with quick-freezing plant, they may be frozen, for example in polythene bags holding about two stones each, and stored on board at low temperature.
As the number of freezer-trawlers increases, so the landings of quick-frozen roes will become larger each year; this note gives advice on suitable methods of processing for both chilled and frozen cod roes.
Fresh cod roes are most frequently sold already boiled to the consumer in this country. Roes suitable for boiling should be undamaged and free from pieces of intestine and traces of blood. After washing they should be covered with lightly salted fresh water and gently boiled for 30 minutes to an hour depending upon the size of the roes. Wrapping in muslin before boiling will sometimes help to prevent excessive damage during the process.
After draining and cooling, the roes can then be either eaten cold, or sliced and then fried, grilled or used as a basis for other prepared dishes.
The nutritional value of fried cod roe is approximately as follows, expressed as percentage weight of edible material:
Protein 21%, fat 12%, carbohydrate 3%; calorific value 207 Calories/100 grams roe.
Roes from newly-caught cod can be successfully frozen and then cold-stored at minus 20°F for periods of six months or longer. The times required for freezing roes are about the same as those for freezing similar thicknesses of white fish. They can be thawed after storage and then used in exactly the same way as fresh roes.
Roes are often a variety of colours when very fresh, ranging from pale pink to dark purple, and these colours are usually retained when the roes are frozen. On the other hand, roes kept in ice for some days gradually assume a uniform pale flesh colour, and since port merchants are more familiar with roes of this colour, the varied hues of roes that have been thawed after freezing sometimes make such roes unacceptable to the trade, particularly since wholesale merchants do not normally boil them before offering them to the retailers; the thawed roes assume the familiar pale pink to putty colour when they are boiled.
Roes frozen at sea are obviously fresher than roes that have been kept in ice for several days; they have no off-odours, whereas a slight smell of hydrogen sulphide, rather like that of a stale egg, is often noticeable from chilled roes that are not very fresh.
Both chilled and frozen consignments on landing often contain numbers of broken roes, due either to careless gutting or to rough handling; methods of utilizing both broken roes and frozen roes whose colour makes them unacceptable to merchants handling chilled roes are described later.
Roes should be fresh and firm, but not too ripe, and should be handled with care to prevent bursting the skins. Roes become softer as they ripen, and often appear more translucent.
After an initial washing in cold water, the roes should be salted either by brining or by drysalting.
Brining: In 70% pickle, times of up to one hour for roes of about two pounds in weight are usually sufficient to give a suitable salty product.
Occasionally treacle and some spices are added to the brine to impart special flavours to the product.
Drysalting: This is the more usual commercial method. The roes are packed between layers of salt in boxes up to about two feet deep for 6 to 8 hours, depending on the size of roe and the degree of saltiness required.
Up to 15% by weight of water is extracted during the drysalting process. The roes are usually firmer when drysalted than when brined.
Surface salt should be removed by thorough washing in large-mesh baskets in cold water. The washing should be repeated, in a change of water, several times during a total washing period of about 15 minutes, in order to prevent unsightly crystallization of the salt on the surface of the roe during smoking.
Dipping and Draining: Roes that have been drysalted are often wrinkled and it is usual to dip the roes into very hot, almost boiling water for a minute or so to restore their plumpness by causing the roes to swell and fill out the skin.
Occasionally a small amount of kipper dye is added to the hot water at this stage in order to ensure uniform colouring of the roes.
The roes can be hung by string tied between the lobes, provided the roes are firm, or alternatively they may be laid over narrow racks or speats or laid on wire mesh trays. The first method is least likely to mark the product. The roes should be left to drain for about half an hour before smoking begins.
Smoking: The roes are cold smoked at a temperature of 90° to 100°F for from 4 to 8 hours, depending on size, in a mechanical kiln, using fires of suitable hardwood chips and sawdust; all the fires should be lighted. In a traditional kiln, smoking may take from 12 to 24 hours.
The loss in weight during smoking is about 20% of the original weight, sometimes as high as 25%.
The final product is usually dark red in colour, firm and easily sliced, and will have lost perhaps 30% or more of its original weight.
Smoking of preserved roes: Roes that have been properly quick-frozen and stored at minus 20°F for periods of up to 6 months will give an equally acceptable smoked product when thawed out and treated as described above.
Roes that have been kept in barrels in 80% salt pickle at chill temperatures for some months may also be used for the preparation of the smoked article, but in this case the roes require to be desalted in fresh water for a day or two beforehand. They are rather soft and flabby and usually require considerably longer in the kiln, perhaps up to 12 hours in the mechanical kiln or 24 hours or more in a traditional kiln in order to produce a satisfactory product.
Smoked Caviar substitute: The Norwegians sometimes smoke cod roes to make a canned product from the loose eggs. The roes are cleaned, washed and salted in dry salt in a similar manner to that described earlier, but following the repeated washing after salting, they are dried in the open air for as long as 24 hours and then smoked in a conventional kiln for from 2 to 3 days, using a cold smoke.
The dark brown roes are then broken up and the loose eggs packed in barrels and stored in moderately cool storage (55° to 60°F) for 5 to 6 weeks, when they begin to show signs of fermentation. This is stopped by the addition of salt in amounts equal to about 15% of the weight of the eggs, and the product is packed in cans but not sterilized. Olive oil is admixed if the product is too dry. Unsmoked caviar substitute is described under salting.
Roes for salting should be fresh, firm and ripe. They should be washed in a light brine to remove blood and pieces of intestine; only whole roes should be used for long-term storage in salt.
The roes are salted in barrels, beginning with a layer of salt on the bottom of the barrel, and adding alternate layers of roes and salt until the barrel is full, using about 30 pounds of salt to 100 pounds of roe. The roes are left in the closed barrel for 10 to 15 days, then drained and carefully washed in a saturated brine, again discarding any damaged ones.
The roes are then repacked in the same way as before, in clean barrels and using the same amount of salt. The closed barrels should be kept chilled, when the contents will remain edible for a year or more.
Cod roes can also be used in the preparation of caviar substitutes. One method of preparation described in American and European publications is as follows:
The cleaned roes are mixed with 20% of their weight of salt and then packed in barrels. The barrels are filled with 80° brine to prevent exposure and oxidation of the roes during salting. When the salt has struck right through the roes, they are drained and soaked in running fresh water for from 6 to 10 hours to remove excess salt. The roes are then ground and mixed with water so that pieces of membrane can float to the surface and be skimmed off. Alternatively the eggs can be passed through a sieve, leaving behind the membrane and other debris.
The eggs are next churned in an alkali solution (made by dissolving 2 lb 4 oz of sodium carbonate in every 10 gallons of water) and left to soak in it for 15 hours to remove any bitter flavours. The eggs are then hung up in a bag to drain and washed several times with fresh water until the drained fluid no longer tastes alkaline.
Artificial colouring can be made by adding black dye to a gelatin solution (prepared from about 2 lbs of pulverized gelatin soaked in 10 gallons of cold water to which is added about the same amount of hot water until the gelatin dissolves). The dye is added once the gelatin solution has cooled below 77°F, and then the mixture is poured over the roe; the whole is left to stand for 6 hours before the roe is removed from the solution. Some manufacturers mix the colouring matter (often lampblack) directly with the roe.
The caviar substitute is sometimes flavoured with an extract made by treating grated lemon peel with alcohol, or with an extract prepared from mixed spices. The final product may be packed in vacuum-sealed jars or cans, but is not normally heat-processed and therefore should be stored at chill temperature.
Very fresh chilled roes and thawed frozen roes, either whole or broken, are suitable for canning. Chilled roes that are not very fresh may retain some of their slight odour of hydrogen sulphide after they have been canned and therefore should not be used.
The roes should be freed of adherent tissue and washed in fresh water. The eggs are next separated from the skins of the roes either by passing them through a fine mincer, when the skins will remain wrapped around the worm of the mincer, or by stirring the cut roes in a mixer, when most of the skins will become wrapped around the stirring rod. Any small pieces of membrane remaining among the eggs can be removed by passing the eggs through a coarse sieve.
The eggs are next mixed with water and salt. A satisfactory product that is easily removed from the can has been made in this country by adding 15% by weight of water and 1% salt. The empty cans are first sprayed on the inside with peanut oil (Arachis oil) to prevent the contents sticking and are then filled with the mixture. The cans are exhausted, sealed and then heat-processed; suggested processing times are 75 minutes for 10 oz flat cans, 90 minutes for 14 oz tall cans and 105 minutes for 16 oz tall cans, all at 240°F (10 lbs/square inch steam pressure). After cooling, the cans can then be labelled and stored; chilled storage is not necessary.
A Danish recipe describes a similar process for canning roes, but suggests adding 5% peanut oil to the minced roes, together with 1% salt; no water is added, whereas an American method that has been described advocates the addition of as much as 40% water. However, the addition of 15% water has been found to give an acceptable product for consumers in this country and to make the process a straightforward one. The addition of this amount lightens the texture; the resultant product has a slightly pink colour, is firm and slices easily, and can be grilled or fried without breaking.
Fresh and frozen cod roes, whole or broken, can be used to make fish sausage, either in edible cellulose or sausage skins.
The roes are cleaned and the skins removed from the eggs, as described under canning, and then mixed with 1% salt.
The sausage skin is filled with the salted roe, tied off at about 6-inch intervals and cut off. Sausages of about 2 inches diameter require boiling for about 20 minutes. After cooling they can be sliced and then, if a cellulose casing has been used, the skin removed.
Boiled roe sausages will keep for about the same length of
time as ordinary boiled roes, but they can of course be frozen and kept in low
temperature cold storage for lengthy periods; they should be eaten soon after
they have been thawed out.