3. Fish processing characteristics

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3.1 Overview
3.2 Gender roles in fish processing
3.3 Sources of fish
3.4 Traditional methods of fish fermentation
3.5 Salting
3.6 Types of fermentation tanks
3.7 Drying of fermented fish
3.8 Solar driers
3.9 Health hazards and hygienic aspects of fermented fish processing
3.10 Quality evaluation of products
3.11 Spoilage and prevention of losses
3.12 Packaging

3.1 Overview

Many consumers in Africa prefer fish in the fresh state, however, a considerable proportion of the landed catch is preserved by artisanal methods.

The principal fish processing methods in Africa are smoking, salting, sun-drying, fermentation, grilling and frying. The predominant type of fishery product in any particular country is, however, closely related to the food habits and purchasing power of the population. Specific types of fishery products are best suited as the local staple food. Furthermore, due to the lack of a good transport infrastructure for the transportation of fresh fish to remote towns and villages, cured fish is the most convenient form in which fish can be sent to such areas.

In West Africa, hot smoking is the main method of fish processing. However, salting, fermentation and sun-drying are also important fish processing methods. It is estimated that nearly 70 percent of the total fish supply in West Africa is marketed in the smoked or dried form. In the Sudan, on the other hand, nearly 70 percent of the total fish landings is consumed fresh; the rest is cured either by salting, fermentation or sun-drying. Very little of the local fish supply is smoked, except in southern Sudan where smoked and very dry fermented fishery products are very popular among the local community.

The most important artisanal method of fish processing in Uganda is hot smoking. Hot smoked fish is produced on a large scale on the islands of Lake Victoria and distributed to the urban markets. Smaller species such as Rastrineobola argenta and Haplochromis spp. are preserved mainly by sundrying. Tilapia, Alestes spp. and small quantities of Nile perch are salted, fermented and dried along Lakes Albert and Edward in western and north-western Uganda. Salted, dried and fermented products are not particularly popular in Uganda, hence these products are transported to Zaire where there is a ready market.

The principal fishery resources in Burundi are the tiny clupeids Stolothrissa tanganicae and Limnothrissa miodon which together constitute about 80 percent of the total landed catch. The main processing method best suited for these species is sun-drying. Anchovies (Engraulis encrasicolus), which are marine clupeids of a similar small size and are abundant in Ghana, are also preserved by sun or smoke-drying.

Fried fish are very important in some countries in West, southern or central Africa. In Ghana for instance, fried fish is widely consumed with a maize-based staple (kenkey) by many of the ethnic groups living along the coast. Fried Nile perch has, in recent years, become popular in Uganda and Burundi and other fried fishery products are also gaining popularity. In both countries, fresh fish is eaten either as a delicacy served with alcoholic drinks or as a fast food.

3.2 Gender roles in fish processing

Throughout Africa, gender roles are associated with various aspects of post-harvest fish handling and processing. This division differs from one geographical region to another.

In West Africa for instance, women dominate on-shore handling and processing of fish. In Chad, Côte d'Ivoire, the Gambia, Ghana and Senegal, salting, fermentation, sun-drying and smoking are women's occupations. Some women also own fishing boats, but lease them to men for fishing while they process or market the catch. Many women also buy fresh or frozen fish for processing. Women fish processors occasionally hire young men to assist in dressing fresh fish especially during the peak periods of processing.

In Burundi, the Sudan and Uganda, fish processing is dominated by men. In Uganda for instance, a survey of fish processing activities revealed that in one district 82.6 percent of men were involved in fish frying, whilst 78 percent of men were involved in salting, fermentation and sundrying. In recent times, however, the number of women engaged in fish processing in Uganda has increased. In the Sudan, women are not only involved in fish processing but some have their own canoes and are actually involved in fishing as well as the processing of fermented fishery products.

3.3 Sources of fish

Africa is endowed with numerous lakes, rivers and seas. These water bodies constitute a rich source of numerous species of fresh fish for many people.

Smoke dried fish is the most important cured fish product in West Africa (Mali)

Hot smoked fish (Nile perch) from the islands on Lake Victoria are marketed in the urban centres (Uganda)

Fermented and dried fish is a popular product in many West African countries

Fried fish is widwly consumed in southern Ghana

Sun-dried small pelagic fish are popular in Ghana (anchovies, Engraulis encrasicolus), Uganda (Rastrineobola argentea) and Burundi (dagaa, Stolothrissa tanganicae)

Over 80 percent of the fish landings in West Africa comes from the Atlantic Ocean. Theremainder comes from freshwater sources such as River Niger, Lake Chad, Lake Volta and River Shari.

In Burundi, the Sudan and Uganda, freshwater bodies provide the bulk of fish supply. Although the Sudan has a marine coastline, only 3 percent of the annual fish catch comes from the sea. The River Nile (including the Blue Nile and White Nile) provides most of the fish supply. Lake Victoria constitutes the main source of fish supply in Uganda. Considerable quantities are also derived from Lakes Edward, Albert and George. Fish from these lakes is normally salted, fermented and dried for consumption within the locality and also for export (Table 2).

Table 2. Source and Type of Fish used for Fermentation

In West Africa women play a dominant role in on-shore handling, pocessing and marketing of fish...

but in Uganda this is predominantly a male activity.

The major marine species of fish found in West Africa can be classified into three broad categories. The fish of category "A" consists of highly-valued demersal species such as barracuda, threadfin, croakers, grouper, grouper sole, mullet, red snapper, shrimps, lobsters, squid and tuna. This group constitutes about 20 percent of the total annual fish landings. Due to their high value, they are usually chilled or frozen at sea before landing and are normally exported either as whole fish or fillets.

In West Africa, small quantities of these species, which are unsaleable in the fresh form, are fermented. Tuna is not commonly cured into fermented fishery products, however, small quantities of fermented tuna were seen in Côte d'Ivoire. Fermented high-value fish were found to be in a stale or semi-deteriorated state when they had not been chilled at the landing beach or markets.

Over 70 percent of the fish landings in West Africa consists of small to medium-sized pelagic species. The main types being sardinella, horse mackerel, Spanish mackerel, anchovies and shad. These are generally classified as category B fish and their prices are often lower than those of category "A.. This group (category B constitutes the main source of cheap food fish for a large section of the population. Most of these species are smoked or grilled; only small quantities are sometimes salted, partially fermented and dried. At peak fishing season, however, sardinella and other pelagic species contribute the largest proportion of fish landings and large quantities may be salted and fermented.

The species of fish classified as category "C" are hake, kingfish, bonito, skate, scad, mackerel, triggerfish, catfish, sharks, flyingfish, guitarfish, rays, anchovies and other trawl by-catch.

These species are generally cheaper than the others and constitute another source of cheap fish. A considerable quantity of category C fish is salted, partially or fully fermented, and dried. During periods of scarcity, these species become an important source of fish either in the fresh state or cured into salted, fermented and dried products (e.g. triggerfish in Ghana). Fish in this category are not usually preserved with ice at all before landing and may be in a poor state by the time they are purchased for curing. The main source of raw fish processed into fermented products in West Africa derives from this category.

Artisanal fishermen dominate the fishing industry throughout Africa. In Burundi, Chad, Mali, the Sudan and Uganda where fishing is carried out mainly on inland water bodies, almost the entire fish catch is landed by artisanal fishermen. Traditional fishing is also the most important method used on the seas of West Africa. In recent years, however, there has been an increase in the number of medium-sized semi-industrial boats and industrial vessels engaged in off-shore and inshore seining and trawling in West Africa. Artisanal fishermen and inshore boats land the low value, cheaper pelagic species (categories B and C), most of which are cured into smoked or fermented products. The industrial fleets are mainly engaged in trawling for high-value species, usually for export. Their fishing methods lead to the production of a lot of trawl by-catch e.g. squids, sea snail, octopus, triggerfish, etc. which are either discarded at sea or sold as low-grade fish often in a poor state of quality. Consequently, a large percentage is salted, fermented and dried. The high-grade demersal species such as seabream, snapper, croaker, etc. are normally expensive and are sold in the fresh or frozen state. They are landed by both industrial and artisanal fishermen but poor quality or stale fish are down-graded and sold to processors for curing into fermented products.

Rivers, lakes and other freshwater bodies in Africa have common varieties of fish. The predominant species are Nile perch, tilapia, Alestes spp., Clarias spp., Bagrus spp., Hydrocynus spp. and other smaller species of the genera Limnothrissa, Stolothrissa, Haplochromis, Oreochromis and Rastrineobola commonly found in the lakes and rivers of East-Central Africa. In Burundi and Uganda for example, dagaa (Limnothrissa miodon) and ndagala (Rastrineabola tanganicae) are major clupeids of commercial importance. All these species are either salted, fermented and dried (e.g. koobi in Ghana) or fermented and sun-dried without salting.

(Imported) frozen fish are occasionally processed into fermented fish products.

Filleting frames from processing plants are sold to processors for fermentation (Senegal).

The final product: fermented dried filleting frames

In Côte d'Ivoire, Ghana and Senegal, processors buy low-grade frozen fish from cold stores for processing into fermented products.

Another source of raw fish for curing is offal from filleting factories. In Côte d'Ivoire and Senegal for example, offal from filleting factories is purchased and then processed into fermented fish. In Uganda, the bulk of the offal from filleting factories is usually smoked for local consumption. Swim bladders from Nile perch are, however, sun-dried and exported to the Far East.

3.4 Traditional methods of fish fermentation

Different processing techniques are employed in fish fermentation from one region to another. This is greatly influenced by factors such as availability of salt and the food habits of the local people.

Three main techniques have clearly emerged as methods commonly practiced in many African countries. These are:

(i) fermentation with salting and drying;
(ii) fermentation and drying without salting; and
(iii) fermentation with salting but without drying.

Figures 2, 3 and 4 illustrate these techniques which are further described below and also summarized in Table 3.

Examples of traditional methods of fish fermentation in Africa

Figure 2 Fermentation with Salting and Drying

Figure 3 Fermentation without Salting

Figure 4 Fermentation without Drying

Table 3. Local Name of Product and Fermentation Process

Figure 5 Sun-drying Fermented Fish in Chad
Step 1 Drying on grass

Figure 5 Sun-drying Fermented Fish in Chad
(a) Alestes spp.

Figure 5 Sun-drying Fermented Fish in Chad
Step 2 Drying by suspending on sticks (b) Clarias angularis

Figure 5 Sun-drying Fermented Fish in Chad
(c) Lates nuiloticus

Figure 6 Method of Processing Guedj in Senegal Step 1 Fermentation of whole fish in brine

Figure 6 Method of Processing Guedj in Senegal Step 2 Dressing of fermented fish

Figure 6 Method of Processing Guedj in Senegal Step 3 Drying of fermented fish on improved traditional drying rack

Raw fish may be left unpreserved overnight to partially decompose before salting and further fermentation

Large species of fish (shark in this picture) are split and cut into pieces to drain...

...and then carefully washed with a sponge to remove blood clots and other materials.

Figure 7 Traditional Method of Processing Tambadiang in Senegal Step 1 Fermentation of whole fish in dry salt

Figure 7 Traditional Method of Processing Tambadiang in Senegal Step 2 Preparation of partially fermented fish before drying

Figure 7 Traditional Method of Processing Tambadiang in Senegal Step 3 Drying of whole, partially fermented fish

Figure 8 Artisanal Method of Processing Fermented Salted and Dried Fish (e.g. Momone, Ghana; Guedj, Senegal) Step 1 Preparation of fish before salting

Figure 8 Artisanal Method of Processing Fermented Salted and Dried Fish (e.g. Momone, Ghana; Guedj, Senegal) Step 1 Preparation of fish before salting

Figure 8 Artisanal Method of Processing Fermented Salted and Dried Fish (e.g. Momone, Ghana; Guedj, Senegal) Step 2 Salting and fermentation of dressed fish

Figure 8 Artisanal Method of Processing Fermented Salted and Dried Fish (e.g. Momone, Ghana; Guedj, Senegal) Step 2 Salting and fermentation of dressed fish

Figure 8 Artisanal Method of Processing Fermented Salted and Dried Fish (e.g. Momone, Ghana; Guedj, Senegal) Step 3 Drying

Figure 8 Artisanal Method of Processing Fermented Salted and Dried Fish (e.g. Momone, Ghana; Guedj, Senegal) Step 3 Drying

In West Africa processing of fermented fish is usually carried out in the open (Ghana)...

..processing of fessiekh takes place in enclosed sheds, sometimes constructed with cement blocks or wooden boards (Sudan).

Dry salt is aplied on split fish (Ghana)

Dry salt is applied on whole fish (Sudan)

Salting tanks are usually covered with a sack, wooden board or metal sheet during salting and fermentation (Ghana)

(Sudan)

3.5 Salting

The absorption of salt during fish curing results in the removal of water from the flesh to a level that impedes microbial growth and enzymatic activities. When high levels of salt are used in fish fermentation, the primary objective is to select the halophilic micro-organisms which will affect a controlled degradative process on the organic compounds in the fish muscle to bring out the desired flavours in the product.

In the coastal countries of Côte d'Ivoire, the Gambia, Ghana and Senegal, where solar salt produced by the natural evaporation of sea water is readily available and inexpensive, fermented fish is heavily salted.

The use of salt in fish processing may either be by dry salting (krenching) or wet salting. In dry salting, the granular salt is applied directly to the fish either in the gills, on the surface or, in the case of split fish, in the belly. The exudate from the fish may be allowed to drain away or be retained. In the latter case, the fish becomes immersed in the exudate and this is often referred to as "pickling".

In wet salting, the fish is immersed in brine for up to two days or dipped for a few hours. It was observed that some processors who cure fish with brine sometimes reuse the salt solution a number of times. This may be a potential source of bacterial contamination to fresh batches of fish.

Table 4 shows the price trend for salt in the countries of this survey.

Table 4. Price Trend for Salt

In the coastal countries of West Africa (i.e. Côte d'Ivoire, the Gambia, Ghana and Senegal) the price per 100 kg of salt ranges between US$ 10 and US$ 16. This is relatively cheap because the solar salt is locally produced or readily available. This accounts for the large-scale use of salt in the production of fermented fish in the sub-region.

Mali is a land-locked West African country without its own source of cheap solar salt. The locally produced rock salt is very expensive and it is valued for its medicinal properties rather than for food. Mali therefore imports limited quantities of solar salt from neighbouring coastal countries for domestic consumption. For this reason, imported solar salt which is relatively expensive is not used in fish processing. Indeed, it was noted through interviews and observations that from habit Malians consume relatively little salt in their diet and there is a prevalence of goitre in the country possibly due to the low level of iodine derived from common salt.

Chad is a land-locked country in Central Africa without any source of cheap solar salt. The domestic salt supply is therefore imported from Nigeria and Cameroon, hence fermented fish is produced without the use of salt.

The Sudan produces its own solar salt from the Red Sea coast, but due to the long distance, civil strife and the poor road infrastructure, salt is quite expensive at the major fish processing centres which are located along the River Nile. In spite of this, solar salt is used on a large scale for the production of fessiekh but not for other fermented fishery products such as kejeick.

In southern Sudan, where fermented fish is popular, small quantities of salt are sparingly applied to the fish. The raw fish may also be dipped into brine for a few hours in order to minimize the use of salt.

In the land-locked East African countries of Burundi and Uganda, salt is very expensive because it is mainly imported. As a result of this, salted fermented fishery products are not very popular. In Burundi, for instance, salt is not used at all in fish processing. In Uganda, salted dried fermented fish is only produced in the western and north-western parts of the country and most of this product is exported to Zaire. Due to the high cost of salt in Uganda, very little salt is sprinkled on fish during processing.

It can, therefore, be concluded from the above that the main factors influencing the use of salt in fish fermentation are:

(i) its availability in the country;
(ii) its cost; and
(iii) traditional food habits.

These factors also influence the type of fishery product widely consumed by the people in the countries of this survey. In countries where salt is expensive or not readily available, salted fermented fish is not popular.

3.6 Types of fermentation tanks

Various types of containers are used for the salting and fermentation of fish throughout Africa. Some of the tanks identified during the study are wooden vats, concrete-lined cane baskets, round or cone-shaped concrete tanks, rectangular concrete tanks, 200 litre oil drums, plastic or wooden barrels, metal (e.g. aluminium or iron) or earthenware cooking pots, jute or polypropylene sacks, cane or reed baskets.

In the Gambia, Ghana and Senegal, some processors pack the raw fish m sacks or bury them in the ground to accelerate fermentation. It was observed in Senegal that most of the concrete tanks located at the major processing sites were buried in the ground to simulate the traditional method of burying fish during fermentation. Raw fish may also be left on platforms or mats to go stale overnight. During fermentation and salting, the container may or may not be covered. For pickled products, the container is covered with a sack or polythene sheet and weighted down with stones or other heavy objects.

The capacity of the various tanks ranges from about 5 kg (for cooking pots and pans) to about 500 kg for the large rectangular concrete tanks which have two or three adjoining chambers. Table 5 shows some of the dimensions and capacities of different types of fermentation tanks.

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