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4.1. Report of the first preparatory mission on improvement and development of sun-drying techniques in Africa

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- M. Fabre and S. Mihailov


The Mission was staffed as follows: 1 Technology Expert (ML Fabre); 1 Marketing Expert (S. Mihailov) and visited the following countries during July 1983: Ivory Coast, Morocco' Nigeria and Senegal.

The Mission's terms of reference were as follows:



The four countries visited have many socio-economical aspects in common. This is true especially of the three West African countries: Senegal, Nigeria and the Ivory Coast. In fact' some socio-economical factors are identical. It would seem worth while therefore to examine these factors in order to understand better the reasons for the traditional techniques used and in order to propose improvements.



Cash crop products for industrial processing and eventual export are generally grown in large, well organised plantations. This applies to coffee, cacao, pineapple etc. Many horticultural products harvest especially garden vegetables, are produced as a family enterprise on small plots of land and with limited resources. These products are essentially grown for domestic consumption. The products that are used for drying are generally the surplus of fresh fruit and vegetables not consumed at harvest time. They constitute a reserve stock for off-season consumption. Small quantities, fresh or dried' not used for domestic consumption' are sold on local markets by women in order to obtain cash. These quantities are generally limited to the weight a woman can carry on her head in a basket, about 10-15 kilos. Most horticultural products are cultivated without the use of draught animals or tractors.



With the exception of Morocco, where women lead a somewhat secluded life, the West African woman has a prominent role in the production, preparation and marketing of horticultural products, especially garden vegetables. It is the women, who take care of the production. They tend the gardens' harvest, prepare the products and sell surplus production. It is for this reason that all efforts to improve traditional techniques should be directed towards women. The extension agent will have to convince women or groups of women about the benefits of proposed improvements.



The diet of African people does not vary much from one country to another. It consists of:

It is important to note this detail since most of the dried products will be used to make this kind of sauce, which the Africans expect to be tasty (abundant use of spices) and often bitter. It should also have a certain stickiness, which the mucilage rich vegetables can give. This explains the great popularity of gombos (okras), baobab leaves and gum arabic in the savannah countries.



Since the Africans are living under climatic conditions that constitute major problems for the preservation of food, they always prefer fresh vegetables and fruits. In most areas, however, especially in those where irrigation is not possible, production and availability of fresh products are limited to the rainy season During the dry season they have to eat products preserved in various ways. Among the various preservation techniques, solar drying is certainly the easiest and the most frequently used. Solar drying is without doubt the preservation method of choice also from a sanitary point of view, provided the drying is done properly and the finished product stored under satisfactory conditions.



While peasants cat with complaisance their own home-grown dried products and while other people living in small rural communities readily buy dried products on the local markets, the consumer living in bigger towns or cities is often reluctant to buy such "farm products", which somewhat disdainfully are considered "picked products", always sold in dried form (leaves, seeds, various fruits picked from wild plants) and not always having an attractive appearance.

Improvements in quality and packing may help to open up new markets in towns, where the consumer may be happy to find products reminding him of his native village. The flight from rural areas to the cities is a major problem in Africa. This tendency, although having many adverse aspects, may offer the farmers new markets for dried products.

The case of mediterranean fruits (grapes, figs, plums, apricots, dates) is different. These fruits are considered "noble" calorie-rich products (dates are more noble than figs). Their consumption is offer linked to moslem traditions and they are eaten in great quantities to break the fast during Ramadan.



With only a few exceptions, dried products are generally vegetables or fruits. The dried products are often ground into powder, usually by pounding. This reduces their volume and consequently also the need for storage space. Ground products are also easier to add to the traditional sauces. Grinding also ensures complete dehydration and thereby better conservation. Dried products are often mixtures of different fresh products ground together and dried in ball shapes (onions and tomatoes, peppers and tomatoes, bissap and tomatoes etc.).

Both fresh and sundried products are used for making sauces but the quantities of dried products used are always smaller than fresh products.

Consequently the off-season diet is less balanced and contains less vitamins and minerals. The dried, ground products are purchased in very small quantities (by grams) on the local market.

Certain imported concentrated products (Maggi seasonings, dehydrated soups and tomato concentrates) are also used for the preparation of sauces. The development of dried vegetable production will, therefore reduce costly imports and improve the diet of the African people in quality as well as in quantity.

Flow chart of harvested fruits and vegetables

With very few exception the role of middlemen, merchants (bane banes) is limited because the quantities available for sale are limited; in addition, collection of the products is often difficult owing to bad road conditions. Nevertheless a certain quantity of dried products finds its way to the markets of larger communities.



Many dried products were found to be of unsatisfactory quality. Dust contamination seemed to be the most important problem. Some products contained stones and soil, suggesting that sorting-out and pre-treatment procedures have been deficient. In some cases the products seemed to have been prepared from over-ripe fruit and vegetables or from fresh produce in different stages of ripeness. More serious were damages caused by rodents, insects and mites, probably due to improper packing and storage.



In most cases drying techniques are very simple: the sliced or diced raw products are simply exposed to the sun on all kinds of flat surfaces, for example flattened or swept ground, roofs or terraces of buildings, flat rocks, roadsides and even railway platforms. The products to be dried may be placed on rocks, mats, corrugated iron or on trays made of a variety of materials: wooden sticks, split bamboo canes, fishing nets, jute bags etc.

Pre-drying procedures include, in some cases, washings with saline alcaline solutions (ashes) and even with fatty emulsions, which result in better colour conservation and quicker evaporation of water. It was observed in Nigeria that slices of dried gombos kept a beautiful green colour after having been soaked in the juice of green lemons. Shade drying is practiced occasionally.

In some places various vegetables were ground in a mortar before being sundried in small balls for example tomatoes and onions and tomatoes and bissap. The advantage of this technique is that the tomato pulp, which is quite watery is absorved by the fibrous texture of the onions (leaves and bulbs) or by the bissaps (leaves and flowers).



A certain amount of research has already been undertaken in the four countries visited, mainly on processing technologies and various typos of driers. Experiments have been done with the following types made of locally available material: tent driers, box driers' cabinet driers and seesaw driers.

Officials in charge of development programmes in the visited countries have also made efforts to encourage the establishment of collection centres, which would undertake to process fresh produce as well as packaging, storage and marketing.



The improvements that have to be made will necessarily affect the traditional system but care should be taken not to upset rural way of living, which often reflects excellent adjustment to the environment. The following are the proposed actions for improvement of the present system.

  1. increase of horticultural production. Part of the increased production should be used for sun-drying. The policy of drying only casual surplus of produce should be changed to cultivation of products destined specifically for sundrying.
  2. losses (sometimes 50 %) could be reduced through the use of more efficient techniques. (adequate pretreatment of raw products, improved sundriers, improved storage and packaging)
  3. establishment of small drying enterprises or cooperatives that could produce larger and more homogenous quantities of finished products. This would attract middlemen who could be instrumental in the marketing of larger quantities.

Improved flow chart of harvested fruits and vegetables



The measures to be recommended for improvement of drying vegetal food products in small family farms must be geared towards the following objectives:



The speed and efficiency of drying procedures are related to the extension of the product surfaces exposed to the sun as well as to the underlying volumes of material. It is advantageous, therefore, to cut, slice or chip the product. To this end one should have a cutting board, sharp knives and planes for slicing.

The cut products become vulnerable and fragile. In most cases metabisulphite washings or SO2- fumigation in a closed room or a tent will prevent discolouration (Maillard's reaction) and increase keeping qualities. Various types of easy-to-clean containers can be used: large basins and plastic buckets, big wooden boxes lined with plastic fertiliser bags etc.

Small fumigation chambers can be constructed with locally available materials: turf, clay and sand reinforced with bamboo sticks. The chambers should be sufficiently large so as to accomodate several wooden trays holding the products.



Improved driers capable of rapid drying under dust-proof conditions have the following characteristics:

The farmer should be able to make most of these driers himself using local materials almost at no cost. Only transparent covers will have to be purchased (used fertiliser bags of transparent plastic can also be used).

Some of these driers, in particular one-tray types, are of very limited capacity since only small quantities per drying cycle (515 kilos par m ) can be processed. For that reason it is recommended to use an improved version of the seesaw drier capable of drying larger quantities during shorter time.



The traditional seesaw drier has a rigid, rectangular frame, the length of which being 3 times the width' resting on a support with an axis. This support is oriented north-south and is sufficiently high to allow the frame to be tilted 30 - towards east in the morning and towards west in the afternoon.

The material for drying is placed on a number of trays, which have a wooden frame 100 x 50 cm and a mesh bottom, which can be made of a variety of materials, such as wire netting, old fishing nets, bamboo lattice or any other material that will allow vertical air circulation and maximum evaporation.



The bottom of the drier is made of galvanised corrugated iron sheets reinforced crosswise by wooden planks and lengthwise by two wooden planks, about 15 cm high. The upper surface of the bottom is painted black. Good thermal insulation can be provided by attaching insulation plates made of lignified wood fiber, expanded polystyrene various layers of corrugated cardboard etc. to the underside of the bottom.

The removable trays are placed on top of the corrugated iron bottom either in a continuous row or with space between them, which will result in better heating of the air above the blackened surface of the corrugated iron bottom. In this case the edges of the trays should be propped up with wooden supports.

A greenhouse effect is obtained by placing a transparent plastic sheet over the filled trays. This sheet rests on the raised edges of the trays and is kept stretched by the weight of bamboo canes fixed to the sides of the plastic sheet. When not in use the sheet is rolled around the bamboo canes.

Air circulation is secured by convection (the tendency of hot air to rise), the drier being tilted at an angle of 30 : fresh air enters at the lower end of the chamber formed by the trays and the plastic covering' escaping at the upper end. A 3 m long drier tilted 30 has 1.40 m difference in levels of air inlet and air outlet.

Air circulation can be improved still more by making the air outlet opening wider (28 x 50 cm) than the air inlet opening (15 x 50). In this way the room enclosed by the drier bottom and the plastic sheet widens gradually from air inlet to air oulet . This will improve convection and prevent the formation of "hot air bubbles" inside caused by air dilatation.



When the products have been dried to such an extent that they will keep, they must be packed, using containers or material ensuring hermetical conditions, e.g. metal containers with suitable lids, polyethylene bags, closed clay containers etc. The packed products should be stored in a dry place and be inspected from time to time.



The quality of the finished product depends, to a large extent on the quality of the raw material which should be harvested at the proper stage of ripeness and transported carefully and rapidly to the site of drying. In addition, good quality of the finished product requires careful sorting' washing, cutting or slicing and dipping in dust (and dust) proof conditions.

Eventual grinding and pounding of finished products should be done as late as possible in the storage period because of the difficulty in detecting alterations and damage in powdered material.



There are many advantages in carrying out drying operations in small size collection centres situated in rural areas and managed by small producers, farmer's associations or even privately owned enterprises capable of handling large quantities of products. The methodology of setting up and operating such centres or enterprises is described in the Report of the Second Preparatory Mission.



The findings of the Mission permit the following statements:

• the low purchasing power of the farmers call for simple and cheap solutions making use of locally available materials and utilising local craftsmen's ingenuity and skill
• local customs are almost always based on sound principles and should be respected
• horticultural work is mainly done by women in many African countries
• the over-all production of dried products is at present relatively small. Also the units offered for sale to consumers at local markets are small, usually available as unweighed heaps of little more than 10 grammes

SEESAW DRIER (In cm) and continued

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