Introduction
The raw material
Preparation
Salting
Draining
Smoking
Packing and storage
This note describes the selection of salmon for smoking, its pretreatment, including gutting, filleting and salting. the smoking process itself, and subsequent packaging and storage for the UK home and export market. There are many variations of the method, hut the procedures described here are typical of good UK commercial practices.
Chilled whole salmon, kept for about 24 hours in ice after capture until they have passed through rigor, or thawed whole salmon that have been properly frozen and cold stored can be used to make a good smoked product. Fish with a high fat content are preferable. Either Atlantic salmon, Salmo salar or Pacific salmon, Oncorhynchus species, can he used; the finished product from either can at the present lime (1980) be labelled smoked salmon, hut draft regulations are in being which propose restriction of the name smoked salmon to the product from Atlantic salmon. It is recommended that smoked fish made from one of the Pacific salmons he labelled accordingly, for example smoked coho salmon or smoked red salmon.
First the whole fish should be carefully gutted and the belly cavity cleaned out. The contents of the belly cavity can constitute up to 25 per cent of the weight of the fish as caught. Congealed blood in and around the main vein along the backbone should be removed; a large spoon is often suitable for this purpose. The belly cavity should then be well washed.
Although salmon fishermen are reluctant to cut or gut a fish, gutting of any fish soon after capture generally ensures release of the blood before it coagulates, thus reducing bruise marks and preventing much of the blood discoloration all too often subsequently found on the cut surface of a fillet.
After gutting, the head is removed by cutting round inside the gills, then breaking or cutting through the backbone. Two single fillets, often called sides, are cut from the headless fish, each complete with nape or shoulder bone, and belly flap. The nape bone gives strenght to the fillet during handling, and provides support if the fillet is to be hung for smoking, although most fillets nowadays are smoked on trays. The belly bones and covering membrane can be carefully removed from each fillet to enhance appearance, although some smokers prefer to leave them on. As much blood as possible is removed from veins by pressing them gently inwards, and any blood on the surface of the fillet is wiped away with cold water; blood left on the fillet becomes black and unattractive in appearance when the fillet is smoked.
Salt can be added to salmon fillets either by brining or by dry salting. Some claim that brining gives a better gloss, but almost all processors prefer dry salting because subsequent drying time in the kiln is shorter.
Dry salting If a fillet is subsequently to be hung for smoking rather than laid on a tray a loop of string is tied through the shoulder under the nape bone before the fillet is immersed in salt. Three cuts are made that just penetrate the skin on the fillet, each 3-5 cm long across the width of the fillet at the thickest part to allow uniform salt penetration, the slits being packed with line vacuum dried salt: as an alternative some processors remove two circles of skin 2-3 cm in diameter.
Fillets are laid skin side down on a bed of salt 2-3 cm thick in the bottom of a box and covered with salt to a depth of about 1 cm at the thickest part and reducing to a light sprinkling at the tail to assist uniform penetration. Additional alternate layers of fillets and salt can be laid on top of the first layer until the stack is complete. The fillets are left in salt for up to 36 hours depending on size to achieve a salt content in the finished product of at least 2-5 per cent; typical times in practice are about 12 hours for fillets from a 4 kg salmon, and 24 hours for fillets from an 8 kg salmon, but the time will vary to some extent depending on initial quality and fat content.
Salted fillets are washed in cold water to remove surplus salt from the surface and ideally are then immersed in 30° brine for 1/2 hour depending on size to even out the salt distribution. By this stage the fillets should feel firm and springy, rather like bacon, when pressed with the fingers, having lost the stiffness they had when taken out of dry salt.
Fillets lose up to 9 per cent by weight during dry salting as the pickle drains away. In some proprietary cures small amounts of brown sugar, molasses and rum are introduced during salting to give a distinctive flavour, but the majority of curers use only vacuum dried salt.
Brining This method is now seldom used commercially because there is no loss of weight during brining, and as a result drying time in the kiln has to be almost doubled to achieve the same total weight loss as for dry salted fillets.
Cuts are made in the skin in the same manner as for dry salting, and the fillets are immersed in 80° brine. 211 g salt/litre water for a number of hours depending on size; typical times are 6 hours for fillets from a 5 kg fish of high fat content and 3-4 hours for the same size fillets with a low fat content.
The salmon fillets, after dry salting or brining, are either hung on (enters by means of string loops through the shoulders or are laid on trays made of plastics coated or stainless steel wire mesh. Hanging has the disadvantage that it tends to stretch a heavy fillet and cause its flesh to gape. Brined fillets sliould be left to drain, preferably in a chillroom at about 2° C, for at least 4 hours before being loaded into the kiln.
Most UK salmon smokers prefer a medium cure, with a combined weight loss during salting and smoking of 16-18 per cent.
Hardwood sawdust, preferably oak, should he used to impart a pleasant flavour to the fish. The sawdust should be clean and free from wood preservatives or contaminants such as paraffin and other lubricants sometimes used on sawblades when cutting hardwoods. Sawdust containing particles of plastics laminates should never be used for smoking fish, since the fumes can be toxic.
In a mechanical kiln The kiln temperature is kept initially at 27°C and the fillets, laid on trays or hung on tenters, are smoked slowly to prevent overdrying of the cut surface and formation of a hard pellicle; residence time is usually 4-10 hours depending on size and fat content of the fillets. The kiln temperature is raised to 33°C for the last 15-20 minutes to bring oil to the surface of the fillets and give them an attractive appearance. Fillets from a 4-5 kg fish of high fat content typically require about 6 hours in the kiln. Salmon fillets generally acquire a sufficiently smoky flavour and enough colour after 5 hours; the smoke supply should then be cut off, leaving the fish to dry for the rest of the time, with the main fan and chimney fan still running.
If fillets on removal from the kiln are found to be too soft and flabby, they should either be returned at once to the kiln and drying continued, or they can be left to sweat, perhaps overnight, and then returned to the kiln for further drying at 27°C, with again a final period of 15-20 minutes at 33°C to bring out the oil.
The finished product should have a consistency rather like that of boiled ham, not too dry and fibrous, and be easily sliced.
Dry salted fillets should lose 7-9 per cent of their weight during smoking, to give the required total loss during salting and smoking of 16-18 per cent; brined fillets, which lose no weight during brining, need about twice as long in the kiln to give the same total weight loss.
In a traditional kiln Smoking time in a traditional chimney kiln is not predictable, because the process is less easily controlled, but a residence time of up to 48 hours is typical, and for large fillets during unfavourable weather the time can be as long as 60 hours. Some processors reduce the total time by hanging the fillets in a drying room heated to about 20°C for up to 24 hours before submitting them to a dense smoke. The finished product is rather more moist than that recommended earlier.
The finished product is a valuable one, and should be well protected by suitably attractive and hygienic packaging. Vacuum packing gives good protection against dehydration, rancidity and contamination, and looks attractive, but it also provides conditions in which toxin-forming bacteria can grow if the product is kept warm. Vacuum packs should preferably be distributed frozen; if they are stored and distributed unfrozen they should always be kept chilled below 4°C for safety, since the product is eaten raw. Smoked salmon is marketed either as complete fillets or in slices.
The shelf life of chilled smoked salmon is 5-6 days in good
condition; the pack should display a use-by date. Frozen smoked salmon, well
wrapped, will keep in good condition in cold storage at - 30°C for at least
6 months.
