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- The processing of smoked fish involves the following processes:
Salting
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Fish is salted either by mixing with solid salt or by immersing in strong brine.
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Size of the fish, fat content, whether the fish is whole, gutted, split or cut, presence or absence of skin and other requirements in the end product etc. are the factors considered in determining the duration and type of salting.
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Depending upon the concentration of brine there may be an uptake or loss of water in the fish.
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Most common concentration of brine employed is 70-80 per cent.
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Fish salted in 100 per cent saturated brine is not preferred as it is likely to make the product unattractive because of the powdery, unattractive, crystals of salt that may be left on the surface.
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In weaker brines longer periods of immersion are needed and there will be an uptake of water, which will have to be evaporated during drying.
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Salting is adjusted that the fish takes up 2-3 per cent salt which is the optimum requirement in many smoked fish.
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However, when the fish is dry - salted the uptake of salt will be very high.
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Such fish are soaked for several hours in water before smoking to bring down the salt content to the desired level.
Hanging
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After salting the flesh of the fish will be moist.
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Surface proteins will dissolve in the brine yielding a sticky solution.
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For efficient smoking fish must be dry enough with no free water on the surface.
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Free water can cause condensation of the distillation products, particularly tar, which leave dark brown colour in the product.
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During hanging the sticky solutions dries on the surface and makes the skin glossy.
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However excessive drying will prevent the fish from acquiring a proper smoky flavour.
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Drying can be done in open air or a hot air drier or even directly in the smoke chamber by burning wood without producing smoke.
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Split and salted fish should remain in stretched out position for uniform exposure of all parts to smoke.
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Hanging is done in several styles depending on the fish handled and the end product desired.
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Fish like sardine meant for canning after smoking are threaded through the eyes.
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Large split whole fish like salmon are suspended by the tail and kept flat open by means of sticks or skewers threaded through the flesh.
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Fish can be hung or even spread on wire mesh trays, however, care has to be taken to ensure that the mesh does not leave excessive mark on the skin or flesh.
Smoking process and types
Cold smoking
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Cold smoking is still carried out in more or less the conventional style, mostly using traditional chimney kilns.
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Fish is kept hung or spread in mesh trays in an upward draft of smoke produced in the floor by the burning fire.
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In the initial stages the fish is moist and the smoke is highly humid.
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Under these conditions use of high temperature will invariably result in cooking of the fish flesh.
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To avoid this, the temperature inside the chamber should not be raised to the maximum employed in the process.
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In the second stage, when the surface of the fish is considerably dry, the temperature inside the chamber could be raised to a level that the fish species concerned will tolerate.
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However, it is desirable to complete the process at the same temperature throughout.
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The highest output of good quality products is achieved when the temperature, relative humidity and the quantity of ventilated smoke are maintained in the correct proportion.
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During smoking the fish dries as also absorbs the aromatic substances from the smoke.
- The relative humidity inside the chamber also is a decisive factor in determining the quality and output of the products.
- RH above 70-80 per cent will considerably slow down the drying and smoking process.
- To control the RH of the smoke, the flame dampers may be kept open thus providing a good draught whenever the per cent RH goes beyond the required level.
- Cold smoking is generally carried out at temperature not exceeding 40oC.
- Duration of smoking extends to several hours, say 36-72 hr.
Hot smoking
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Several designs of kilns tunnels are available for hot smoking fish.
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The fuel is burnt either directly inside the kiln on movable trolleys or in external hearths located near the tunnel.
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The fish is charged into the tunnel in cages.
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The chamber will be having a metal frame structure and brick walls and can hold a number of fish cages.
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In contrast to cold smoking where cooking of the flesh is neither the aim nor is attained in any case, in hot smoking fish is dried and cooked in the kiln before it is smoked.
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Drying is done in an intense draught of hot air at 75 to 80oC produced by burning fire.
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The skin of the fish becomes dry while flesh becomes cooked as well.
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At this stage the fish is considered ready for smoking.
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Smoke is produced by covering the burning logs with saw dust and the temperature in the chamber is maintained at or above 100oC.
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A schedule of operation in hot smoking can be considered as drying at 75 to 80oC for an hour followed by smoking at 95 to 100oC for another one hour.
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The requirements will vary with the size and species of fish.
Other methods
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In addition to cold smoking and hot smoking, there are other methods. They are
Use of artificial colouring
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It is often difficult to achieve uniformity in the product, particularly colour, in smoked fish.
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Even if near uniformity in colour can be achieved, batch to batch variation occurs.
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One way of overcoming this inherent deficiency of smoking process is to artificially colour the fish with permitted dyestuffs in the brine used for salting.
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Vegetable dyes, coal tar dyes etc are so used, the selection being dependent n the type of the product
Post process handling
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