Utilization of Bonga (Ethmalosa fimbriata) in West Africa - 6. Bonga processing


6.1 Sun-drying of fermented and salted bonga

6.2 Roasted, salted, and dried bonga (ketiakh)

6.2.1 Ground roasting
6.2.2 Parpaing roasting

6.3 Bonga smoking

6.3.1 Barrel oven
6.3.2 Open banda ovens
6.3.3 Closed banda oven
6.3.4 Chorkor oven

In West Africa, bonga is consumed fresh, smoked, cooked, salted and dried, or fermented, salted and dried. Food habits, purchasing power, and infrastructural facilities influence the type of product in particular areas. In the past, very little bonga could be marketed fresh and the fish had to be preserved for wider distribution.

This study identified hot smoking of bonga as the main method of bonga processing in the countries visited. The fermenting, salting and sun-drying of bonga occurs only in Senegal and The Gambia. Roasting, salting and drying (ketiakh) occurs in Senegal only.

6.1 Sun-drying of fermented and salted bonga

Fermented and salted bonga is sun-dried to reduce the water activity and that slows down and stops the growth of the micro-organisms responsible for spoilage. The salting reduces the moisture content in order to ensure a longer shelf-life. The shelf-life is normally reduced by blowflies that attack products with a high moisture content.

The warm dry climate of Senegal and The Gambia provides a wind and sun combination that facilitates the drying of the fermented and salted bonga and its re-exposure to sunlight during long storage. This climate differs from the humid climate of the more southern coastal countries of the sub-region which makes fish rapidly re-absorb moisture and develop moulds.

At the southern Senegalese coastal site Kafountine and several coastal centres in The Gambia the bonga that is left over from sales to the fresh bonga traders and the smokers is bought mainly by women processors. These women leave the bonga in vats, metal pans or baskets overnight for fermentation. The fermented bonga is then gutted. The gutted fish is washed in seawater or fresh water collected in cement tanks (The Gambia). The belly cavity of the rinsed fish is heavily salted and more salt is sprinkled on the fish's body. Heavy salting of the fish occurs during the rainy season when flies are more abundant, and light salting in the dry season. The fermented and salted bonga are then placed on the racks to dry in the sun.

The racks are constructed from cement and bamboo lattices or wood and rhun or oil palm branches. The raised platform and the gaps between the lattices or branches provide good ventilation from the wind. The cement or wooden supports are between 40 and 100 cm off the ground. Unlike the scattering of fish on sandy beaches or grass near fishing camps or fishermen's compounds, these racks protect the fish from contact with the unclean ground. This makes the technique hygienically good. The fish are also easily protected from the rain by a plastic (polyethylene) sheet spread over the racks.

Figure 6 Fermented bonga being gutted (Tanji, The Gambia)

Figure 7 Fermented bonga drying on racks (Tanji, The Gambia)

Except for the relatively expensive cement input for some of the support pillars, all the materials required for the racks are cheap local inputs. The only problem with this technique is the salt component. Salt is not always available and prices vary between the dry and wet seasons. When available, local salt is mediocre in quality and contains impurities. Its quality discolours some of the fermented, salted and dried bonga products.

Drying takes three days during the dry season and five days during the wet season. When dry, the product is protected from insect attack and can be stored for up to two months without physical or economic losses.

6.2 Roasted, salted, and dried bonga (ketiakh)

Ketiakh is the most important processed fish product in Senegal. The name also applies to processed sardinella which contributes the greatest quantity of the ketiakh produced. The product is appreciated by urban and rural consumers as a source of animal protein on their rice or other cereal-based meals. Of the bonga landings about 40 percent is utilized in ketiakh production. The Thies region of Senegal produces the largest quantity (see Table III).

This product was introduced over 30 years ago by a prominent fishing group, the Lebous, of the Cap Vert region of Senegal. Only fresh bonga is used in the process and competition with the fresh bonga traders is high. It is either cooked through roasting on the ground or through the traditional oven (parpaing).

Table III Ketiakh production in Senegal

Region Production (t)
1986 1987 1988 1989 1990 1991
Dakar 991 1,059 863 619 524 619
Thies 103 14,608 15,527 14,013 13,443 15,745
St. Louis 10,342 24 56 90 175 152
Ziguinchor 0 0 0 0 0 0
Fatick 0 37 28 5 8 14
Kaolack 43 0 0 0 0 0
Louga 0 0 0 0 0 0
TOTAL 13,465 15,728 16,474 14,727 14,150 16,530

Source: Résultats Généraux de la Pêche Maritime Sénégalaise, DOPM; Ministère de l'Equipement, des Transports et de la Mer. July, 1992.

6.2.1 Ground roasting

The fresh bonga is collected by donkey cart or plastic pans and transported to the ash-filled soil area next to the landing beach. The fish is then arranged in rows by experienced workers (mostly men). Half-dry leaves of the Combretum species of shrubs are placed on the fish. The heap is then covered with dry grass, millet stalks and/or dried bark of the baobab (Adansonia digitata) tree. The pile is then sprinkled with a mixture of scales of previous peeled-roasted bonga and ashes to compress the heap for protection against destructive wind effect and for efficient roasting.

The roasting continues for at least two hours and the roasted bonga is left on the soil overnight to cool. The skin is then peeled off and the fish are gutted. The nicely cooked and peeled bonga is then salted and dried on raised platforms for two to three days. The dried ketiakh is then stockpiled and sold by weight. The average price is FCFA 75 per kg.

The grass and leaves from different wild shrubs are more available than millet stalk which is only available during the dry season, after the millet harvests. The baobab bark is also readily available, but the slow growth of the baobab tree makes it rather scarce and unreliable as a source of fuelwood. The limited available resources of local plant material used for roasting are further threatened by the Sahel's persistent drought.

Figure 8 Bonga being unloaded from a cart for roasting on the ground

The continuing use of the same area for roasting creates a very unhealthy condition for processing the bonga. The muddy and very black soil condition during the rainy season gives an even worse sight and base for roasting the bonga.

Apart from the unsustainability of the fuelwood source, the process also produces very thick smoke that covers a distance of up to 3 km in Mbour. The pollution caused by this created hostility between the women processors and the townsfolk, who have persistently complained about the situation. However, the women processors, who are realizing a good economic return from the process, seem to have a good political lobby that is giving them support.

The obstinate women have turned down an offer from the fisheries authorities in Mbour to move their roasting to "parpaing" ovens at Mballing (3 km from their present site). Their technique, meanwhile, remains crude, unhygienic, environmentally menacing, and unsustainable in the medium term.

Figure 9 Bonga roasting at Mbour (Senegal)

Figure 10 Drying peeled and salted roasted bonga (ketiakh)

6.2.2 Parpaing roasting

The "parpaing" oven is a covered combustion chamber with at least two front openings for the fuelwood and a metal grill on top. The openings are usually covered with metal plates to control the fire. The typical one used in Senegal is 3 m x 1.25 m x 0.8 m.

The bonga is arranged on the grill top in very close rows in a belly-down way. The heads of each successive row fit between the tails of the two before. Once the fish have been stacked, the fire is lit beneath them. The fire is then controlled by opening and closing the openings and by occasionally dousing it with water. The wood used is mainly filao (Casuarina equisetifolia) and acacia (Acacia seyal).

The fish is then hot-smoked for between four and  thirteen hours, with frequent turning to expose all sides of the fish to the process. After the cooking ,the bonga is peeled, gutted, salted, and dried as ketiakh. This method of producing ketiakh has filtered into The Gambia through the Senegalese community who reside there. The modified Chorkor ovens are used to hot-smoke the bonga before the peeling, salting, and drying.

The "parpaing" oven roasts and smokes bonga. The process is easier and guarantees a better quality ketiakh than the ground process described above. Trials are continuing on improving this oven and it is now the oven of the future in the bonga-smoking industry of Senegal.

6.3 Bonga smoking

Smoking is a method of fish preservation that combines three effects:

However, the long storage life of the smoked bonga, is due more to the cooking and drying than to the phenols in the smoke.

Smoked bonga is the most popular bonga product in West Africa. The species is harvested in increasingly large numbers and smoking seems to be the best way of preserving the catch, in particular, in the more humid areas between The Gambia and Angola. The catch is generally unloaded from the canoes into baskets, boxes, or plastic basins and either dumped on the beach or transported directly to the smoking houses. Once the bartering ends and the sale is concluded, the bonga is either rinsed or placed directly on the rack of the oven being used. Bonga that has gathered sand when being landed on the beach is usually rinsed before smoking.

In West Africa, local conditions and availability of materials have dictated the design of smoking ovens. The ovens range from the open traditional banda, the covered banda (with flattened barrel metal sheets), the barrel ovens, the mud block covered banda ("Fante"), the Chorkor, to the now modified Chorkor ovens. Despite the variations in the design and materials used, the raw material is invariably fresh, ungutted and unscaled whole bonga and the smoking process invariably consists of a cooking phase in which the raw fish is cooked over a high fire and a more or less long drying phase over a low fire.

6.3.1 Barrel oven

One of the ovens used in the sub-region is made from empty 200 l oil drums. It is relatively light and convenient for individual smokers to move around within the smoking area and between operation sites. The size that makes it transportable renders it unsuitable for smoking large quantities of the bonga.

Figure 11 Barrel ovens in Boulbinet (Guinea)

The maximum capacity recorded at Adiaké (eastern Côte d'Ivoire) is 14 kg. In this area the barrel oven is used to cook bonga for 30 minutes before transferring the fish to "Bodo" ovens (same as the "Fante") for longer periods of smoking. These ovens and the ones at Boulbinet, Koulewondy, and Teminetaye (areas of Conakry, Guinea) are entirely designed from single barrels. A grill or wire mesh is placed on the top of the barrel. The bottom is cut out and placed on the sandy or gravel base. An inlet opening for the wood is then carved out of the bottom of the barrel. The fire is lit and controlled through these openings, after putting the small bonga flat on the top of the barrel. The fish is then covered with old sacks, old cardboard, old corrugated iron sheets, or any material that the, mainly, women smokers deem to be efficient in containing the heat in the barrel chamber.

The oven distributes the heat evenly on the fish being smoked and produces very high temperatures for drying the bonga. The small capacity and easy access to the fire at the bottom of the barrel makes the control of the smoking process easy. One can also avoid the burning and/or over-drying of the product. However, it is not efficient for dealing with the large bonga landings that are common in both Guinea and Côte d'Ivoire, as well as the other countries in the sub-region.

6.3.2 Open banda ovens

The banda is a ubiquitous simple smoking oven in the West African sub-region. Usually it is a table of chain-link wire fencing that is supported from the ground on a framework of mangrove or other available wooden forked poles. Cross-pieces are placed on much stronger wooden or metal bars to support the wire mesh and the fish. The metal bars are more resistant to fire. Although the structure of the oven is the same, the construction materials used, its size and operation differ in Senegal, Guinea-Bissau, Guinea, Sierra Leone, Nigeria, and Cameroon.

The most common support material is the mangrove and the most common platform material is the chicken or chain-link wire fencing, albeit one can find steel pipes and other materials on the open banda ovens observed. The ovens are more reinforced in Sierra Leone and Nigeria where the smokers climb on top of these ovens to stack and turn the fish.

Figure 12 Metal pole supported open banda ovens in the open air at Kamsar (Guinea)

The bonga is stacked on the wire mesh side-by-side in rows and belly-down. The fish assumes head-down angle to the horizontal of about 30°. Once the stacking is complete, the fire is lit mostly using mangrove wood (except for The Gambia and Senegal) beneath the fish. Control of the fire depends on the experience of the smoker. Despite the variations in experience, there are cases of banda frames catching fire and the bonga getting burnt.

Consumer preference in the different countries and local markets dictates the types of smoked bonga products available. Some are fresh-dry and others are hard-dry. Smoked bonga that has lost between 25 and 45 percent of its moisture content is considered fresh-dry and that which has lost 62 to 84 percent is considered hard-dry. The duration of the smoking depends on the type of final product and the type of wood being used. However, the standard heating time for a fresh-dry product is six hours (split into two sessions of three hours). The fresh-dry bonga keeps for a maximum of four days while the hard-dry bonga can keep for up to six months. The hard-dry bonga requires about three days smoking or five fires of at least two hours per session for long storage. It can also be lightly re-smoked as and when necessary during storage to further prolong its shelf-life. Some sections of the banda oven are dedicated to storage and re-smoking over a low fire.

 Except for Guinea-Bissau and Guinea where banda ovens can be found in the open air, the banda ovens in all the other locations visited were housed in dwelling houses (Okoroete, Nigeria) or simple shelters thatched with grass or palm leaves (Guinea-Bissau, Guinea, Sierra Leone, Nigeria, and Cameroon).

Fuelwood consumption of the open banda oven is very inefficient because of the relatively uncontrollable wind effect through the open spaces between the wooden supports. The supports frequently catch fire, the fish gets destroyed and sometimes the whole shelter and even dwelling houses are destroyed by fire in the sub-region (for example, 14 dwelling houses and some banda houses in Canamine, as well as 40 banda houses and some dwelling houses in Melo - all in southern Guinea-Bissau - were burnt down).

The availability of wood dictates the smokers' choice of fuelwood. In Senegal, Acacia seyal, Adansonia digitata (baobab) and Cordyla pinnata are the most popular. The Gambian smokers use Parinari excelsa, Bauhinia thoningii, Daniella oliveri, and Pterocarpus erinaceus. In Guinea-Bissau, Guinea, Sierra Leone, Nigeria, and Cameroon, the main fuelwood is the red mangrove (Rhizophora racemosa). Mango (Mangifera indica) and rubber are utilized in Guinea and Cameroon respectively, even though the effect of sodium acetate used to kill rubber trees in Cameroon has not yet established. Apart from the baobab tree, the felling of all the other trees are of concern to the Forestry authorities in the respective countries. Their regulation and tax levy in some areas, e.g., in Guinea, is creating a shortage of mangroves. The shortage and increase in cost of transportation and cutting labour is increasing the price of fuelwood used by the smokers.

Figure 13 Bonga well stacked on an open banda in Canamine (Guinea-Bissau)

The increasing vigilance of the forestry authorities and the increasing emphasis on the protection of the environment by national governments are making it more and more imperative to find an improved technique for the open bandas. Wastage of fuelwood, fire hazards, the nose, eye and bronchial problems experienced by the smokers, make the open banda technique inappropriate for bonga smoking in the sub-region.

Figure 14 Open banda in a dwelling house in Iko (Nigeria)

Figure 15 Close-up of Figure 14; note bonga on "rackets"

Figure 16 "Rackets": split mangrove roots, tied together by strings made from dried plantain stem

Figure 17 Bonga hanging from wooding sticks pierced through the gills, being smoked in Iko (Nigeria)

Figure 18 Open banda supported by metal and wooden poles

6.3.3 Closed banda oven

Mud blocks, compacted clay or flattened barrel metal sheets are used as walls around a rectangular fireplace. On top of the support is a grill or wire mesh to hold the fish. The walls can vary in height from 50-80 cm. Flattened barrel covered banda types are common in Guinea and Cameroon, and the other types are found in Sierra Leone, Guinea-Bissau, Senegal, and The Gambia.

The stacking, fire controls, and product smoking time relationship are not very discernible between the closed and open bandas. The significant difference is the degree of energy and fuelwood wastage which is higher in the case of the open banda.

Flattened barrel walls

Realizing the inefficiency of the open banda ovens, some smokers cover the sides of their ovens with flattened barrel metal sheets. An opening (stoke hole) is cut in the front of these structures for the input of fuelwood and fire control. The covers have improved the fuelwood efficiency, but the heat conduction through the metal sheets makes the working environment relatively difficult for the smokers.

Figure 19 Flattened barrel banda in Boulbinet (Conakry, Guinea)

These ovens are used in Guinea (Boulbinet) and Cameroon (Mbonjo I) for smoking bonga. Compared to the open banda, this is an improvement which is cheap and efficient.

"Fante" banda ovens

This banda design, mud blocks or compacted clay forming walls around a rectangular fireplace on which a metal grating or wire mesh is placed, was introduced in Sierra Leone by migrating Ghanaian fishermen of the Fante Tribe in 1950. This oven design is also used in Senegal, The Gambia, and Guinea-Bissau, albeit not called "Fante". These ovens consume less fuelwood than the traditional open banda ovens and this reduces processing costs. The use of the openings (stoke holes), for the entry and exit of the processors to the fire area for lighting and controlling the fire, created the unusually large openings found on the "Fante" ovens of Sierra Leone. These openings reduce the efficiency of the ovens.

'Improved Chorkor oven'

In The Gambia a closed banda oven has been developed with partition walls inside (see Figure 22). In order to ensure that the traditional bonga smoking methods are improved to reduce fuelwood consumption and create a better environment for the processors the appropriate technology is required. A fire box (smoking chamber) that can be closed to reduce heat loss and conserve fuelwood and a fixed grill or wire mesh platform for stacking large quantities of bonga for smoke-drying is needed. The appropriate technology was achieved in The Gambia through consultation with the smokers and it is called the "Improved Chorkor Oven".

Figure 20 "Fante" oven with large stoke hole in Tissana (Sierra Leone)

Figure 21 Home-style mud block "Fante" oven in Cacine (Guinea-Bissau)

This oven is built with fire bricks, cement, or mud clay blocks. It stands at 1 m high with a metal fixed rack at a height of 0.8 m. It usually measures about 8 m long, 1 m high, and 1.5 m wide with 12 stoke holes (each 0.5 m wide). The smoking houses have four of these ovens.

The unwashed bonga is stacked on the oven as described for the open banda in Section 3.2.2. The product undergoes 3 or 5 fires of unequal duration according to fresh-dry or hard-dry requirement.

A metal grill is fixed on top of a red brick or mud block walled oven with stoke holes for fuelwood delivery and fire control. Each oven has up to six openings and can take up to 800 kg of wet bonga per smoking session. Smoking periods (fires) range from three fires for 34 days' storage to five fires for up to six months' product storage. The technique, which combines the efficiency of the Chorkor oven with a large capacity, is the bonga smoking technology of the future for West Africa. It has already been emulated in neighbouring Senegal (Kafountine and Diogue) and has also attracted the attention of the IDAF programme in Cotonou, Benin.

Figure 22 "Improved Chorkor oven" in Kafountine (Senegal)

6.3.4 Chorkor oven

The Chorkor fish smoking technique has been proven to be more efficient in terms of cost and energy utilization than the other designs used in West Africa. This technique was developed in 1970 with the help of a FAO project in Chorkor, a small coastal village on the outskirts of Accra, the capital of Ghana. It grew out of the traditional cylindrical oven made from compacted clay, used for the smoking of sardinella. The cylindrical form was modified into a rectangular oven, which was further developed into the now famous Chorkor oven. This oven has mud, cement, red-brick walls with stoke holes for fuelwood inlet and fire control.

Figure 23 Chorkor oven being used for bonga at Bonfi (Conakry, Guinea)

The frame can support up to 15 fish-filled trays stacked on top of each other, thus forming a chimney which can be covered at the top. The heat and smoke are retained and that facilitates heat and smoke circulation around the layers of fish.

The oven is cheap when local materials are used. It is also durable when sheltered and can produce a high quality and uniform product. The success of this technology in Ghana has attracted a lot of interest from technologists and processors in the sub-region. It has been adopted for the smoking of sardinella by all the countries covered in this study. The Chorkor oven has also been introduced to a few bonga smoking centres (e.g., Gunjur in The Gambia, Kaback in Guinea and Shenge in Sierra Leone). The smokers claim that it reduces health problems (eye, nose and bronchial problems) associated with the traditional open bandas. Fuelwood consumption, which is increasingly becoming the major concern of the processors, is also reduced by this technique.

However, the Chorkor oven has a serious limitation for bonga smoking: the standard tray of the Chorkor oven can take only 30 kg of wet bonga (Bonfi, Guinea). With this capacity, it cannot replace the banda for the bulk processing of bonga. The banda can take up to 940 kg wet weight or a tonne when stacked by a well experienced processor. The Chorkor can only be effective in smoking a relatively large quantity when the bonga is laid flat on numerous trays. Otherwise the fish will get squashed by the trays above when the bonga is packed as on the bandas - side by side in rows belly-down. Therefore, the Chorkor oven is not suitable for large quantities of bonga smoking when the fish are supposed to be closely packed in the banda style.