3.7 Drying of fermented fish
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Sun-drying is the final, yet an important, step in the traditional method of fish processing in many African countries. With the exception of fessiekh, mindeshi and terkeen in the Sudan, as well as certain types of wet fermented fish in Ghana, most fermented fishery products in Africa are sundried to reduce the water activity and therefore slow down or stop the growth of the micro-organisms responsible for fermentation or spoilage. Drying is normally combined with salting to reduce the moisture content sufficiently to ensure a longer shelf-life. Products with high moisture content (above 35 percent) are susceptible to attack by blowflies especially if the salt level in the product is low. This results in the development of maggots in some fermented fishery products during storage. At low moisture content (below 15 percent) the product is brittle and prone to fragmentation and attack by insects such as dermestes.
Table 5. Dimensions of Various Types of Fermentation Tanks
|Type of Container||Length (cm)||Width (cm)||Height (cm)||Thickness (cm)||Diameter (cm)||Maximum Capacity (kg)||Country|
|Cone-shaped wooden vats||-||-||50-80||3-5||Top: 80-100
|Rectangular concrete tanks||100-300||80-150||60-100||10-12||-||500||Ghana, Senegal, the Sudan|
|Round wooden or concrete vats and cement-lined baskets||-||-||80-100||3-5||Top: 80-100
|200||Côte d'Ivoire, the Gambia, Ghana, Senegal|
|Oil drums (half or full)||-||-||75-200||0.1-0.15||75||200||Chad, Mali, the Sudan|
|Earthenware pots and metal pans||-||-||-||-||20-30||10||Chad, Ghana, Mali, Senegal|
|Wooden and plastic barrels||-||-||60-80||1-1.5||50-80||200||Côte d'Ivoire, Ghana, the Sudan|
The equipment used for drying is usually simple, inexpensive and locally available. The raw salted and fermented fish may be spread directly on the bare ground, grass, old mats, nets, stones or raised drying racks. In Burundi, for instance, ndagala is dried on well-designed metal drying racks at major landing centres. The driers, which consist of sloping wire mesh raised about 1 m above the ground, were introduced at the processing centres through a sponsored project. Provision is made for a polythene sheet or tarpaulin as a covering for the during bad weather, rainfall or at sunset. In Chad and Uganda, fish many be by passing a rope or stick through the head to skewer the fish and then by hanging it on wooden beams or drying lines, or placing in on the ground.
The various of artisanal raised drying racks are constructed with local materials such as bamboo, mats, old nets, plam leaves, etc. Sometime, big stones or logs may be used to construct a drying bed usually of about 20-25 cm high. Raised drying platforms may also be used to store fish for several months pending sale or distribution. A lot of locally designed platforms are used on a large scale in the Gambia and Senegal.
3.7.2. Drying process
The process of drying fish in the sun is greatly influenced by the size of fish, whether dressed or whole, and prevailing weather conditions. During hot dry periods, fermented fish may be dried within two to three days, especially if they are small species or cut pieces. Larger species may take four to five days under these conditions. In the wet season, drying is very slow and can extend beyond seven days in some instances. A lot of spoilage is experienced by processors during this period due to the humid conditions and rain falling onto the fish. During the period of drying, the processors spread, carefully arrange or hang the fish on the drying equipment (racks, stones, ground, lines or beams). The fish may be turned once or twice during the day for even exposure of the entire surface to sunlight. In the evenings, the semi-dry product may be collected in a basket or heaped together on the drying platform and covered with polythene sheets or any suitable water impermeable material. In many countries, whole or split but uncut species such as Alestes spp., tilapia and triggerfish are arranged in a characteristic order with all the heads pointing in one direction. The orientation of the heads is changed to the opposite direction when the fish are turned. This, according to the processors, is a simple control measure to ensure that every single piece of fish has been turned.
Processors assess the rate of drying periodically by pressing the fish between the fingers to determine the texture. Fish processors use only sensory evaluation (visual appearance, odour) to determine the quality of their product.
Drying on the ground exposes the fish to pets and other domestic animals such as sheep, goats, pigs, lizards, etc. The fermented dried fishery products may also be contaminated with sand, grass and earth when they are dried on the bare ground. Drying on raised platforms, therefore, gives a better quality product.
In Côte d'Ivoire, the Gambia, Ghana and Senegal, fermented fish processors apply small quantities of edible oil (usually fish oil) over the surface of the fish during drying. Some processors claimed that this is done to give the fish a glossy appearance when it is ready for market, but other processors indicated that the oil prevents blowfly infestation.
3.8 Solar driers
A lot of research has been conducted on other forms of drying for improved results. One of these improved methods of drying is the use of solar driers which may be any of the following: solar tent drier, solar cabinet drier, solar dome drier and solar drier with a separate collecting and drying chamber.
These driers have been found to be efficient by achieving higher drying temperatures and reduced humidities. They also increase drying rates, producing lower moisture content in the final product and highly improved quality. It is possible to attain temperatures as high as 45°C inside solar driers and it has been suggested that this relatively high temperature offers some protection against attack by blowflies, beetles and other vermin. Additionally, solar driers also offer some protection against adverse weather conditions, for instance wet seasons.
Although solar driers have been successful at the experimental level, artisanal fish processors have not found them useful because of the large capital investment required for their construction. Other constraints have been the lack of robustness in most solar driers, the fairly low capacity and the technology needed for their construction which often makes them unattractive to artisanal fish processors. Furthermore, some processors have found the quality of products from solar driers different to that of traditional driers and often unacceptable to consumers.
For some time to come, these improved driers will not be favoured by the artisanal fish processors in developing countries due to the constraints mentioned above.
3.9 Health hazards and hygienic aspects of fermented fish processing
It was observed in all the countries visited that certain processing practices constitute health hazards to consumers, processors and the environment. These practices relate to dressing, washing, salting/fermentation, drying and waste disposal of the fish, as well as the use of poor quality salt and curing containers.
(i) Dressing: It was observed in Ghana and Senegal that fish may be held under the foot on the ground during dressing. This practice can cause microbial contamination of the fish and injury to the processor either from the spines of the fish or by the knife.
(ii) Washing: This is a very essential stage in fish processing but in almost all the countries visited it was noted that potable water is often not available. Therefore, water from lagoons, rivers, lakes or seas is used to wash the fish. These water bodies are often polluted by domestic waste, making them a possible source of chemical and microbial poisoning.
(iii) Salting/Fermentation: The non-use of salt results in uncontrolled fermentation. Under such conditions, the fish muscle becomes ideal for the growth of pathogenic organisms and the product may decay within a short period. Such products could pose a health hazard to consumers. The reuse of salt may also lead to contamination of fresh batches of fish with micro-organisms.
(iv) Drying: It was generally observed that fish is often dried on the ground except in the Gambia and Senegal where raised drying racks are extensively used. Drying fish on the ground is a source of contamination with sand and micro-organisms. It also renders the fish prone to attack by pets and other domestic animals such as goats, sheep, pigs and rodents. It was also observed that fish is not covered during drying which leads to attack by blowflies especially for unsalted fish or in cases where salting is inadequate. Another environmental hazard associated with drying fish is the strong offensive smell associated with fermented fish. This is pronounced during drying, hence processing sites are often located near fish landing sites or further away from living places.
A typical fermented fish processing site in Senegal
Fish is sometimes allowed to remain immersed in the brine formed during alting and fermentation
Weights such as stones are placed on top of the fish to keep them completely immersed in the brine
Cane baskets lined with cement are used for fermentation in Wesr Africa; they are low and buried in the sand in Senegal...
...they are high and standing on top of the sand in Ghana.
(v) Waste Disposal: At most of the processing sites in the countries of the survey, and indeed in many other African countries, there are no efficient of disposing of offals and other waste matter. These items are indiscriminately thrown away, thus polluting the environment and the available water body as well as serving as suitable breeding grounds for flies and mites which eventually infest the cured fishery product.
(vi) Salt Quality: Solar salt which is predominantly used for curing is often dirty and stored in heaps or in sacks on the bare ground without being covered. Solar salt is a major source of halophilic bacteria which causes poor quality fermented fishery products notably "pink.".
In Ghana and Côte d'Ivoire where salt is sometimes reused, particularly in the processing of triggerfish, the brine becomes a source of contamination by osmophilic moulds which are noted to cause the kind of spoilage in salted/fermented fishery products known as dun.
(vii) Containers: The fermentation tanks used for curing are not usually easy to clean due to their rough surfaces. These containers, therefore, become sites for the growth of microorganisms and sometimes blowfly maggots.
3.10 Quality evaluation of products
The quality of fermented fish is assessed subjectively by visual and/or organoleptic inspection. The main quality parameters are texture, colour, odour and fragility.
(i) Texture: Two main types of textural characteristics were identified in the study. Fermented fish intended to be used as food fish is hard dried or semi-dried but firm. This was the main type of fermented product found in many African countries (e.g. guedj, koobi, ewule). Due to the firm texture it remains whole in the sauce after cooking. In Côte d'Ivoire, the Gambia, Ghana and also in the Sudan, fermented fishery products with a soft texture are produced. These products are commonly added to soups and sauces in small quantities as a condiment. Fessiekh is used both as a food fish and condiment. It is either minced, mashed before adding to the vegetable sauce or broken up completely during cooking.
(ii) Colour: The colour of the product depends on the species of fish used as well as the processing method. For whole products such as fessiekh, a silvery appearance close to the fresh product is considered high quality. Poorly fermented products tend to be grayish or dark Fermented products which are split and dried are usually light brown in colour. Long storage and further drying darkens the product. Yeet, for instance, becomes dark brown after weeks of exposure to the sun.
(iii) Odour: The odour of fermented fishery products varies from mild to very pungent. Soft, semi-dry products usually have a strong smell but very dry fermented fishery products have a mild odour.
(iv) Fragility: When fermented fish is dried to a very low moisture content, it tends to break up during packaging and storage. Soft or semi-dry products become flaky especially if the raw fish is putrid or fermentation is unduly prolonged. Momone, for example, breaks up if poorly cured.
Drying of fish on the ground exposes by domestic animals, rodents, lizards, etc.
Drying on grass and nets
Drying on elevated rachs (Burundi - a sponsored project)
Dressing small fish on the ground by holding the tail under the fot can be a health hazard to processors an to consumers.
Dressing on a platform reduces contamination and wearing gloves protects the processor against injuries.
(v) Shelf-life: The shelf-life of fermented fish is an important quality characteristic. At high moisture content or low salt levels, insects tend to lay eggs on the product which eventually develop into maggots and destroy the fish. Very dry fermented fish without salt is easily infested by dermestes species. Dry fish can be stored for nearly six months, but the soft or semi-dry ones have a shelf life of up to three months.
3.10.1 The role of fish inspectors and quality control certificates
Considering the microbiological changes which occur during fermented fish processing and the possible adverse health implications, there is a need for effective quality control of these products.
All the countries visited have government institutions responsible for inspecting fish and fishery products to certify their wholesomeness. In many of these countries, however, this role is limited to the collection of production statistics on landed catch or quantities of fishery products imported or locally produced, possibly for the purpose of computing tax to be paid. Fish inspectors are also involved in identifying the various fish species landed.
In countries where large quantities of fermented fish are produced and exported (e.g. the Gambia, Senegal and the Sudan), certain quality standards are set. Similarly, countries which import cured fish also have quality standards for fermented fish. The major quality factors are moisture content, salt level, organoleptic characteristics (colour, smell), microbiological quality, insect infestation, packaging and texture. In the Gambia, Mali, Senegal, the Sudan and Uganda, fish inspectors are stationed near processing sites or at major marketing centres to assess and certify the quality of all cured fishery products before distribution. It is almost impossible to transport cured fishery products from major processing centres in the Gambia, Senegal and the Sudan, especially if the product is intended for export.
Generally, quality standards are not clearly defined, they are difficult to assess and impossible to analyse due to a lack of relevant equipment. Official quality certificates usually report on visual characteristics and tend to be subjective.
Fish inspectors are mainly involved in the collection of production statistics, species identification and the provision of extension services to fishermen, processors and traders at the market in order to ensure the safety of fresh and cured fishery products.
Côte d'Ivoire: The Fisheries Department is empowered by government legislation to critically examine all fishery products imported into the country. Even though there is a large-scale local production of cured fishery products, fish inspectors are not actively involved in the inspection of locally produced fishery products.
The Gambia and Senegal: These countries export considerable quantities of fermented fishery products, hence there is an important role for fish inspectors. They are well trained staff who are located at the major fish processing towns. They carry out visual inspections to assess quality parameters such as texture, smell, colour, insect infestation and mould growth. Quality certificates are then issued with regard to the wholesomeness of the product.
Ghana: There is little emphasis on the inspection of locally produced fermented fishery products because production sites are scattered and virtually inaccessible by road networks. The Extension Service Department of the Ministry of Agriculture, however, provides assistance to processors on improved processing practices. For imported fishery products, officers from government agencies such as the Port Health Department, Customs, Excise and Preventive Service, Ghana Standards Board and Fisheries Research and Utilization Unit visually inspect all incoming fermented fishery products at the ports of entry to certify the quality before distribution.
Mali: The inspection of ail types of cured fishery products is handled by the officials of "Operation Pêche at Mopti. They inspect all types of dried fishery products arriving at Mopti Port which is the main commercial centre for fishery products. The examination is mainly visual and the parameters assessed are insect and mould infestation, texture, colour and visible signs of spoilage. Quality certificates are issued by the inspectors for any cured fish that arrives at Mopti. The officials are also involved in providing extension services to the fish traders to reduce post-harvest losses.
The Sudan: The Fisheries Administration of the Sudan is charged with the responsibility of inspecting and ensuring that fessiekh is produced under hygienic conditions and that the quality meets specified standards of texture, smell, colour and packaging before export. As was observed in other countries, facilities for an objective assessment of quality are lacking, the main method of quality assessment being visual inspection.
Uganda: The Fisheries Laboratory of the Ministry of Animal Industry and Fisheries (MAIF) is responsible for the inspection and certification of fresh and cured fishery products. fishery products cannot be exported to Europe, Hong Kong, Kenya and Zaire without quality certificates. The Ministry of Animal Industry and Fisheries has trained officials at the major markets to inspect all incoming cured fishery products and to advise traders on good handling, display and storage practices. They ensure that cured fishery products are well stored in warehouses provided by the government specifically for this purpose.
3.11 Spoilage and prevention of losses
It was observed in all the countries that various factors were responsible for spoilage of fermented fishery products.
3.11.1 Types of spoilage
Hard, dried fermented fishery products were found to be susceptible to common spoilage factors such as fragmentation, mould growth, insect infestation and attack from rodents.
Soft, semi-dry fermented fishery products normally suffer from maggot infestation and mould growth. These problems are especially prevalent when salt levels are low or final moisture content is high. Blowfly attack starts during drying because the fish are not covered. Eggs are rayed on the fish which later cause spoilage.
3.11.2 Causes of spoilage
The following were identified as the main causes of spoilage in fermented fishery products:
(i) Fragmentation: This is due to over-drying and poor handling practices during storage and distribution;
(ii) Mould Growth: This results from high relative humidity or high water activity of the product due to insufficient drying;
(iii) Insect and Maggot Infestation: This is often due to low salt levels in fermented products or high moisture content which enables blowflies to lay eggs or maggots on the fish. At low moisture content dermestes also attack fermented fishery products;
Dressing of fish and disposal of offals and domestic waste at the beach attracts domestic animals and flies (a)
Dressing of fish and disposal of offals and domestic waste at the beach attracts domestic animals and flies (b)
(iv) Microbial Spoilage: Microbial deterioration was observed in fessiekh produced in the Sudan. This was attributed to the use of bruised fresh fish, insufficient salting during curing as well as improper handling. Processors therefore inspect the products during packaging and sort out the deteriorated ones.
3.11.3 Preventive Methods
The commonest method of preventing spoilage in fermented fishery products in many African countries is periodic redrying. In Mali, the wet fish is immersed in K-Orthrine or Gardona for a few minutes before drying to prevent blowfly attack. Some processors also apply various types of insecticides to fermented fishery products during sale and distribution. Mats used for packaging fish and warehouses are fumigated with malathion. To prevent rodent attack, raised platforms are frequently used for the storage of cured fish and the product is covered with mats. it has also been reported that the finished product is heaped onto a mat on the ground inside a room and surrounded with dry powdered pepper which is believed to ward off insect attack.
In Chad there is a prevalence of indiscriminate use of insecticides such as Lindane, Gammalin 20, Shelltox, DOT as well as Gardona. Some processors in Ghana have also reported the application of camphor (napthalene granules) as an insecticide to fermented sun-dried anchovies in storage.
Packaging forms an important part of food processing because it facilitates handling during storage and distribution within the marketing chain. To achieve the expected results from a packaging material, it must possess certain characteristics such as adequate strength to protect the packaged product from damage at economic cost, it must be readily available and easy to use, and should be clean to prevent contamination with undesirable substances.
Table 6 shows that baskets, old jute bags and polysacks form the most widely used containers for packaging fermented and sun-dried fishery products either for storage or during distribution.
In Mali, straw mats and ropes are used to wrap and tie fermented dried tilapia. It is only in the Sudan that empty vegetable oil cans or kerosine cans and polythene bags are used for the packaging of wet fermented fish (fessiekh) for export and local retail trade respectively. In Uganda, grass is used in addition to baskets to package cured fish.
The preference for simple artisanal packaging materials in all the countries surveyed is attributed to their low cost, convenience of handling and ready availability in the locality.
Most of these packaging materials are reused a number of times before they are discarded. It was observed that packaging materials such as baskets, ropes and mats have a life-span of 612 months. The oil cans, jute bags and polysacks can last for two to three years.
The major disadvantage of these packaging materials include the fragility of baskets, and the inability of cleaning them easily after use to prevent recontamination of the products. Baskets and sacks do not offer any barrier to insect infestation and rodent attack, nor are they impervious to water or other fluids. As a result of the above, products stored in baskets, mats or sacks are susceptible to rapid deterioration if exposed to rain.
Figure 9 Fumigation of Storage Mat with Malathion (Mali)
Figure 10 A Typical Storage Platform for Dry Fermented Fish (Mali)
Figure 11 Dipping Fermented Fish in a Solution of K-Orthrine prior to Drying (Mali)
Table 6. Packaging Materials of Storage and Distribution
|Country||Type of Packaging||Advantages of Packaging||Disadvantages of Packaging||Lifespan of Packaging Material|
|Burundi||Jute bags, polysacks||Cheap, easy ventilation and convenient for handling||Possible insect infestation; fragmentation due to improper handling||Up to 3 years, but greatly influenced by level of usage|
|Chad||Jute bags, polysacks||As above||As above||2-3 years|
|Côte d'Ivoire,||Baskets, jute bags, polysacks||As above||As above and fragile for baskets||6-12 months (baskets); 2-3 years (others)|
|The Gambia||As above||As above||As above||As above|
|Ghana||As above||As above||As above||As above|
|Mali||Ropes, mats, jute bags, polysacks||As above||As above||Up to 12 months (ropes and mats); 2-3 years (others)|
|Senegal||Baskets, jute bags, polysacks||As above||As above||6-12 months (baskets); 2-3 years (others)|
|The Sudan||Old oil cans, polythene bags, jute bags, polysacks||As above||Exclusion of air may lead to growth of pathogens (cans)||6 months (oil cans); disposable polythene bags; 2-3 years (others)|
|Uganda||Baskets, grass, jute bags, polysacks||As above||Poor hygiene and same as Burundi||1 month (baskets and grass); 2-3 years (others)|
Fermented dried fish may be packaged in baskets...
...or tied with ropes and wrapped with straw mats for distribution.
In Sudan fessiekh is packed either in kerosine tins...
...or in labelled polythene bags.
Jute sacks are commonly used to package dry fermented fish for export in the region
Old cardboard boxes are used to package cured fish for domestic distribution.
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