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4.2 Report of the second preparatory mission on sundrying techniques in Africa
- E. Espiard and S. Mihailov
The Mission was staffed as follows: 1 Technology Expert (Etienne Espiard); 1 Marketing Expert (Serge Mihailov) and visited the following countries during August and September 1983: Sudan, Kenya, Zaire' Upper Volta.
CONCLUSIONS
The sundrying technique used in the visited countries is still a traditional one by direct exposure to the sun on racks or sometimes directly on flattened ground. Consequently, the quality of the product is very poor and dried products are consumed only when fresh products are lacking.
The solar driers where the material being dried is directly exposed to the sun and protected against dust from the air and rainfall by a transparent cover (glass or plastic) did not improve the aspect of the product.
In all the countries visited, the mission did not hear of or see any case of indirect solar drying which would have given dried fruit and vegetables of first class quality. The few good quality products found on the market came from industrial drying plants using diesel oil for artificial heating.
A considerable market exists for dried products. Numerous products' (especially vegetables) dried in the traditional way' are marketed on a regular basis in the so-called semi-desert countries, such as the Sudan and Upper Volta, and this market could be expanded with products of better quality (better looking and more hygienic).
The African market will, largely, remain a market for poor customers, who could barely pay for quality. Therefore assistance should be given to help promote marketing of products of improved quality.
Indirect sun drying, which can only be used for green or pigmented vegetables and for fruits, can easily be developed in the visited countries because numerous farmers, in remote areas, could produce more vegetables, fruits and spices if they were assured of an outlet for their dried products, which are less perishable than fresh produce and need not be transported rapidly.
In the small garden plots near the cities and also on the market, great quantities of unsold products could be saved by sundrying. Taking into consideration the rainy season with abundant supplies and the dry season with shortage, sundrying is a good way of saving surplus production for the dry season.
RECOMMENDATIONS
It is recommended to:
Demonstrate that it is possible to produce good quality dried vegetables, keeping the colour and the taste of the fresh product, with sundriers easily manufactured at the family and/or industrial level. For this purpose 5 projects (out of 9 identified) have, as an objective, information and training.
Participate in the development of new irrigated agricultural areas which cannot profitably produce fruit and vegetables for fresh consumption, due to the distance between the production sites and the food consumption centres and/or lack of a fast transportation system.
Supplement these two operations with a marketing program aimed at promoting a sales strategy for these products, which could be considered "new products", because of their superior quality.
IMPORTANCE OF FRUIT AND VEGETABLE LOSSES BETWEEN PRODUCTION AND FOOD CONSUMPTION
The FAO publication "Food Loss Prevention in Perishable Crops" (1981) gives the main conclusions regarding this question.
- their humidity is high (70 to 95%)
- the rate of respiration is high to very high. Calories production vary from 0,5 to 10 million joules per metric ton and per day at 0° C, and from 5 to 70 million joules/mT/d. at 20°C
- their texture is fragile and does not withstand piling-up (crushing even in small boxes).
- from 15% to 50% in developed countries, depending upon the type of product, the climatic conditions, the way of harvesting and the packaging, transportation and distribution process;
- from 20% to 60% in developing countries, especially in tropical areas.
In general it is considered that average loss is 40% and this has been confirmed during the mission, except in the Sahelian countries where the losses are lower because people practice traditional solar drying. The Upper Volta authorities estimate their vegetable losses at 20% only.
The world horticultural production is evaluated at 1.200 million metric tons i.e. as much as cereal production.
In other words, the fruit and vegetable losses could be evaluated at 500 million metric tons for this one sector.
Any system that will save part of the production can have a very important effect.
WAYS OF SAVING CROPS
The aforementioned FAO publication outlines the following measures that would contribute to the production of losses:
TENDENCIES IN DEMAND AND MARKETING OUTLOOK FOR DEHYDRATED FRUITS AND VEGETABLES
Urban centres in Africa have developed much more rapidly than the birth rate (already very high) has increased. While total average demographic growth is around 3% per year, urban centres have developed by 7 to 10% due to rural migration. The new urban populations can generally be divided in two groups:
Group A = wage earning minority with some purchasing power (maximum 25%)
Group B = "floating' majority with low purchasing power (minimum 75%).
Each group has distinct purchasing and consumption habits that must be taken into consideration in promoting a product.
Group A (well-off people)
Group B (low income)
PRESENT NEEDS
Products that are consumed in addition to the basic starchy food are fresh or dried vegetables, leaves, gombos, chilli, to which sometimes tomatoes, onions or even potatoes are added. Dried tomatoes and onions are generally in powder form which makes them liable to adulteration. Various substitute products are imported, such as Maggi and Liebig sauces and "cubes", tomato concentrates, etc.
PROSPECTS
There is already an open market for dried products. It could be developed by expanding production of new dry products (not yet dried in the traditional way). For example:
a) Same product but of higher quality
To meet consumers' needs pertaining to Group A (well-off), products should be as attractive (presentation, packing) as substitute products.
Depending upon the retail price, consumers from Group B (low income) could also buy improved dried products' especially in periods of shortage when prices of traditional products are too high for them.
b) New dried products
Products, such as tomatoes and onions, very much in demand when fresh, but seasonal and expensive, are much used in manufactured products (imported tomato concentrate' Maggi sauce) should be able to take a place in the market in a dried form provided that they are properly processed. Dried fruits could also be commercialised as delicacies.
c) Packing
In order to protect the product and enhance its commercial value' it should have an appropriate low-priced packing.
For this purpose packages should be small - 10 to 50 grams. corresponding to quantity needed for a sauce. The catering package for sale of large quantities could also be launched.
SUN DRYING
Sun-dying of agricultural products, such as leaves' flowers, fruits, seeds, vegetables, roots an tubers, as well as meats and fishes is generally used in most hot countries, mainly in African sahelian or semidesertic countries. The mission found that this was the case in Sudan and Upper Volta. With the exception of tobacco and tea drying in the Sudan, sun drying is generally done under very poor conditions. Fresh products are exposed directly to the sun without any preparation and without dust protection; they are exposed to ultra-violet radiations' which discoulour chlorophyl and carotene and brown the products (Maillard's reaction).
Several research centers or institutes ("Karen Center" in Kenya, "Institut Voltaïque de l'Energie" in Upper Volta ...) are testing new solar driers with dust protection' but the mission did not see any drier operating with external air heaters.
Drying by wood burning (another form of renewable energy), is mainly used for meat and fish and also to some extent, for cassava or plantain bananas (seen on the Kinshasa market) but, rather surprisingly, this type of drying is little or not at all used in countries with abundant forests.
DRIED PRODUCTS - QUALITIES AND DEFICIENCIES
Appendix 1 gives an exhaustive list of fruits, vegetables, leaves, roots and tubers seen on the markets. Cereals, maize, corn and oil seed containing more than 20% oil (including palm nuts, peanuts, soya seeds) are excluded from this list.
The quality of these products is far from uniform. It is good for the usually dry vegetables (beans, lentils, peas, chick peas, full medams ...) and low for leaves, flowers, fruits and vegetables with the exception of:
Most of the green or red products were discoloured and browned like tossed hay. Furthermore' all products contained a high percentage of foreign matter (sand and dust). However, we did not see any products with parasitic insects or mites. Nevertheless' these products seemed to have kept their nutritional value.
Sun-drying, even with the actual techniques, remains one of the best ways of saving seasonal surplus production and to ensure supplies between abundance periods. Sundrying also makes transport of the produce from production to consumption centres easier.
The cost of tin-plate and the difficulties in obtaining it in Africa is a restraint for the development of the canning industry.
The lack of facilities for transporting frozen goods is a considerable restraint for the development of the frozen food industry.
Minimum quality standards of sundried products should be as follows:
DRYING PRINCIPLES
Sun drying of leaves, flower, fruits, vegetables, roots and tubers requires the application of the following principles:
- increasing the exposed surface of the products (dicing' slicing' spreading-out of products),
- catching as much as possible of sun radiation by appropriate absorbers (black plates perpendicular to the sunbeams),
- increasing the circulation of air around the product,
- avoiding heat loss (insulation of areas not exposed to the sun)
- avoiding direct sun radiation of the product since this affects the appearance adversely (discolouration).
- rehydradration
- dust contamination
- harmful effect of light
SUN-DRIER CLASSIFICATION AND TERMINOLOGY
Sun-driers are classed according to the systems of heating the product:
In the specially constructed driers' the raw products are spread out in an enclosed space where they are protected against dust contamination and subjected to a controlled air flow. There are various types of such driers:
Direct driers can be used for several products as seeds, roots' tubers or some fruits as red pimentos' but they are generally the cause of many disappointments and we recommend strongly to use indirect or mixed driers, which ensures much better drying conditions.
DECRIPTION OF AN INDIRECT DRIER (see Figure 1 - Indirect solar drier showing external air heater, cabinet drier with trays and chimney for extraction of humid air.)
The indirect drier has three main components:
External air heater. A good air heater consists of an enclosure' rectangular in cross section. The ceiling of the enclosure is a transparent sheet allowing the sun rays to heat the black painted bottom.
The drying cabinet. Can be a simple cupboard shaped chamber with doors facing north. The cabinet can hold several trays placed on racks or trolleys. The hot air from the external air heater enters the cabinet through an opening at the bottom, rising through the mesh trays with the vegetal products towards the top.
Humid air extraction and eventual recycling. The top of the cabinet has a device for extraction of the hot humid air with possibility of recycling in case the air is not completely saturated with humidity. Extraction of air can be effected through:
Controls and analysis (indirect driers). It is considered advisable to check the temperature and humidity of heater inlet and outlet air, air in contact with the products and drier outlet air.
In addition, residual humidity of dried products should be analysed and total weight of ingoing and outgoing products should be recorded.
Various types of direct and indirect driers are shown in figures 1 - 6.
MANUFACTURERS OF DRIERS
CANADA
- BRACE RESEARCH INSTITUTE
MACDONALD COLLEGE
800 SAINT ANNE DE BELLEVUE
Dryers type 1 and 4
THAILAND
- INTERNATIONAL DEVELOPMENT
RESEARCH CENTER (I.D.R.C.)
ASIAN INSTITUTE OF TECHNOLOGY
QUEBEC HOA 100 CANADA
P.O. BOX 2754 BANGKOK
Dryers 2 and 5
FRANCE
- ETS CAUSTIER
ROUTE DE PRADES
6600 PERPIGNAN
- associated with the
CENTRE D'ETUDE SUR LE SECHAGE SOLAIRE
from PERPIGNAN UNIVERSITY
AVENUE DE VILLENEUVE
66025 PERPIGNAN
Dryers type 1, 3, 4, 5
- UNION TECHNIQUE D'AQUITAINE
U.T.A.
VILLENEUVE SUR LOT - Dryer type 2
INDUSTRIAL PROCESSING
The following considerations apply only to small size enterprises situated in rural areas and managed by small producers or farmers' associations.
ORGANIZATION AND OPERATION
The following points are relevant:
LOCATION
Location of an enterprise should be chosen according to the availability of the following resources and facilities:
MEASURES FOR SECURING SUFFICIENT QUANTITIES OF RAW MATERIAL OF ADEQUATE QUALITY
The enterprise cannot function unless delivery of a minimum quantity of raw material of adequate quality is secured. This necessitates the adoption of a regulation to be observed by members of the association or cooperative in question. This regulation should specify:
Privately owned plants should include the same requirements in delivery contracts. Payments for delivered products should always be based on quality and quantity.
COLLECTION AND TRANSPORT OF CROPS
Only fresh and suitably ripe products should be collected. Fruits, onions, tomatoes and peppers should have a high dry matter content. Delivery to the plant should take place shortly after harvesting. Care should be taken that the products suffer no bruises or other kind of damage during transport.
Wooden crates for transport should be of suitable construction. Soft wrappings should be used for fragile fruits.
The conditions of delivered partially dried products should be defined: softness, caking' ratio of fresh and partially dried weight etc. Such precautions will ensure homogeneity of dried products as well as continuous and full use of plant installations.
Transport of products can be improved by the use of better vehicles and equipments, e.g. wheel barrows, specially fitted bicycles, small carts with rubber tyres, pack-saddles adapted to the wooden crates used etc.
CONTROL OF DELIVERIES
Purchase price of delivered products should be based on quality and quantity. Quality control may be an incentive for farmers to produce better quality products.
QUALITY
Quality control should include: determination of dust damage, foreign matter and defect products, residual humidity and an evaluation of processing qualities.
Periodical testing of samples in specialised laboratories would be useful as a current control of the reliability of testing done in the plant.
QUANTITY
The delivered products should be weighed on scales. Estimates of volumes are unreliable.
PREPARATION AND TREATMENTS
Some treatments are difficult to carry out by the producer and can be done better in the collection centre. Insecticide fumigation involving the handling of methyl bromide or phosphine is dangerous and is economical only if large quantities are treated.
FUMIGATION
The technique of choice consists in covering piles of crates with a plastic chute. Air-tightness is secured by heaping sand or rail on the edges after the required amount of aluminium phosphide has been introduced. This kind of treatment can be done in the open air with negligible risks.
PRETREATMENT
If drying or partial drying is done by the producer treatments for colour preservation must be done immediately after slicing or cutting and before the product is placed on trays.
Blanching and sulphitation are done by rapid soaking in boiling salt water with potassium metabisulphite added, in a large tub that can be heated by fire. The unstable pigments of green products such as chlorophyll in gombos, herbes, etc. will be stabilised in this way and browning due to Maillard's reaction will be reduced to a minimum. This treatment is not absolutely necessary for carotene rich products, such as tomatoes and peppers, whose pigments are more stable.
STABILIZATION BY SO2 - FUMIGATION
This treatment, recommended for white grapes, apricots and white figs, can be done easily by placing the loaded trays inside a plastic tent in which sulphur is burnt.
The work involved in treating larger quantities of produce in the collection centre can be rationalised, for example by the use of a stainless steel tank mounted on a fireplace, baskets lifted by pulleys and moved on suspended rails, in a room with concrete floor with drainage.
DRYING
The type of equipment to be used is related to the kind of product to be dried and the operations involved (complete or partial drying).
Complementary drying above 60 requires a drying cabinet with trolleys, artificial heating and forced ventilation.
DESINSECTIZATION AND STORAGE
Products considered sufficiently dry to prevent fermentation and fungal growth should be packed in such a way that they are protected against dust, noxious animals and against regaining of humidity. The stored products should be kept in complete darkness to avoid damage by photophile insects. If necessary, fumigation (with insecticides) of the packed products can be carried out in plastic tents or in drying cabinets.
PACKING
Some products are sold in powder form. For the reasons mentioned previously, pounding and grinding should be done at a late stage, preferably immediately before marketing. Pounding with a morter gives a better product than mechanical grinding in a mill, of which there are various types, but requires more labour and often also sifting.
Packing for consumers can be done at little cost. Products sold in polyethylene bags can be weighed on small scales. Packings should carry indications of nature of the product, net weight and origin. This information can be printed or stamped on a label placed visibly inside the bag (not to be used for powdered products). Polyethylene bags can be closed with scotch tape.
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