|Small-Scale Processing of Fish (ILO - WEP, 1982, 140 p.)|
|CHAPTER III. FISH SMOKING AND BOILING|
The smoking procedures given below apply to specific fish or fish types. As a general rule, these methods can also be applied to fish of similar shape, size, fat content, etc. Cold smoked products are not described in detail here as they are generally unsuitable for developing countries (for detailed methods, see FAO, 1970).
Figure III.4. Modified version of traditional oven - Ivory Coast kiln
(a) Slide view
(b) Top view
(c) View showing smoke baffle. Fish holding racks rest on top of this structure when operating
Notes on construction details for the Ivory Coast kiln
1. The walled enclosure is approximately 1 m high and 1 m2 or 2 m2 in plan section (Figure III.4 shows a 2 m2 section).
2. Into one side of the enclosure is set the fire-box. This is most easily made from one or two old oil drums. For small kilns of about 1 m2 two 20 gallon drums are sufficient. For larger kilns, 44 gallon drums will be needed. The drums are set on their sides so that an open end protrudes a few centimetres outside the square at ground level, the rest of the drum being inside the enclosure. The end of the drum inside the square remains closed, but a hole about 0.3 m2 is cut in the uppermost surface of the drum. The square cut in the upper surface of the drum must be located centrally with the outer enclosure.
3. A square baffle sheet is suspended, above the hole in the oil drum, by wires from each of the four corners of the enclosure. This baffle consists of a sheet of iron, about twice the dimension of the hole in the drum, which has holes of about 1 cm diameter punched approximately 4 cm apart. The height of the baffle above the opening must be adjusted in use until a good distribution of smoke and heat is obtained.
4. The fish themselves are supported on racks above the enclosure. The racks are made from 7.5 cm square timber and chicken wire or expanded metal. The size of the racks is exactly the same as the square dimensions of the enclosure. The racks will rest on top of the walls of the enclosure and on top of one another. Four or five racks of fish can be smoked at once.
5. During smoking, the upper rack should be covered with sheet metal or damp sacking; metal sheet is preferable for protection against rain.
The procedures for short term preservation do not involve a long drying stage. It is important that the processor knows whether a short or long storage period is required so that the initial smoking technique can be varied accordingly. Fish smoked at very high temperatures and dried will be very brittle in texture. In commercial practice, accurate temperature measurement and control is not generally easy. The small scale processor should try to adjust smoking temperatures so that well cooked moist products and non-brittle dried products are made.
I.6.1. Hot smoking - smoked shark products (Short term preservation)
A method for smoke drying shark is given by FAO (1978). The various steps are briefly summarised below:
- The shark should be gutted and bled immediately after capture.
- After removal of the fins, the skin should be removed by stripping off from head to tail (flaying). The skin can be salt cured and subsequently sold for making leather.
- The flesh should be cut into 10 cm square pieces which are then brined for 30 minutes in a solution containing 10% salt and 2% vinegar. The purpose of the vinegar is to suppress the development of ammoniacal odours from the high residual urea content of the flesh.
- The shark muscle should be pre-dried for 1-3 hours to form a surface skin.
- Smoking should be initially carried out at a temperature of 70-80° C for one hour.
- The temperature should be lowered to 60-70° C and smoking then continued for another 1.5 hours when the product is immediately cooked. This product is very liable to spoil at ambient conditions and should be kept frozen or chilled.
For improved storage characteristics at ambient temperatures, the product should be further dried either in a smoking kiln or in the sun.
I.6.2. Hot smoking - buckling (Short term preservation)
Buckling is a hot smoked product made from herring although other similar fish such as mackerel could be substituted. Medium-sized fresh fat herring are processed as follows:
- To rinse the fish in fresh water to remove blood, slime, scales, etc.
- To place the fish in 70-80% saturated brine for 2-3 hours.
- To rinse the fish in fresh water and string them up on sticks which are placed through the eyes or gills and mouth.
- To pre-dry the fish on racks in the sun for 2-4 hours.
- To build up a fire with little smoke and a bright clear flame. To place the fish into the kiln and allow the temperature to rise up to 70-80° C. This takes approximately 1-1½ hours.
- To cover the fire with wood chips to produce heavy smoke and maintain the temperature at 60-70° C for about 1½ hours. The racks should be changed around from time to time.
A weight loss of 20-25% is normal and the product can be kept for 1-2 days at ambient temperatures.
I.6.3. Smoking in an oil drum kiln (After Watanabe and Cabrita, 1971) (Short term preservation)
- The fish are first washed, scaled, split dorsally and the guts removed. They are washed again, and then placed in a saturated brine for between 30 minutes and 2 hours depending on the weight.
- After a further washing, the fish are sun dried on a rack, skin side downwards, for 2 days or until a 25% weight loss has been achieved.
- The fish are hot smoked on racks in the smoke drum by using a short connecting pipe (1 m from the fire box) and a temperature of 90-100° C. The fish are smoked for 3-4 hours or until they are brownish-yellow in colour.
- Following smoking, sun-drying is carried out for up to 2 days in order to reduce the fish to 35-40% of their dressed weight.
Products made with this smoking method can have a storage life of 2 months or more.
I.6.4. Hot smoke drying of bonga (Ethmalosa spp.) in the Altona kiln (after Clucas, 1976) (Long term preservation)
- The fish should either be well iced or brought ashore and processed within 6 hours.
- The use of fish boxes is recommended. Keeping the fish out of direct sun light by the use of, for example, wet canvas sheets is of great importance in terms of maintaining freshness. Where ice is available, this should be used.
- The fish should be washed in clean running water, or 10% brine to remove slime, blood or any foreign matter. Bonga are not normally headed or gutted for traditional and aesthetic reasons.
- The fish should be hung on wire rods pushed through the cheek bone, leaving small gaps in between the fish to allow the passage of smoke.
- A suitable fire wood, for example, red mangrove, should be cut into 10 cm pieces and arranged in the fire box close to the opening. The fire can be regulated by covering the hole in the fire box with a sheet of corrugated iron. The smoke rising up into the smoke box eventually fans out through small holes in the top of the box. At the start of the process, a low smouldering fire is required.
- After loading the fish into the kiln, the fire should be lit and the temperature for the first 2-4 hours, depending on fish size, maintained at 80° C. For the next 2 hours, it should be raised to 90-110° C to cook the fish. It is then reduced to 80° C again until a sufficiently dry product has been obtained (8-18 hours). Product yield should be in the range or 23-30% with a corresponding moisture content of 8-12%.