3.0. Post Harvest Handling and Processing of Green Coffee in African Countries.
Coffee growing and trade have exceptional importance in the economies of many countries, which are largely dependent upon this commodity for their export earnings, and thus for the continuation of their development programme in the social and economic fields. All coffee-growing countries fall into the lower-income and middle-income nations of the world in terms of annual average GNP per capita. At least 20 coffee producing countries are classified as least developed countries (LDCs).
Coffee is grown and exported by more than 50 developing countries, but the major consumers are all industrialised countries, The United States of America, Europe and, more recently, Japan. Globally, coffee is the second major traded commodity to oil and thus plays a vital role in the balance of trade between developed and developing countries, providing the latter with important source of export earnings to pay for imports of capital and consumer goods.
In 1986, when the world coffee trade was subject to a system of export quotas for producing countries, 17 of these countries were dependent on coffee for more than 25 percent of their total export earnings; of these 9 less developed countries (LDCs) received more than 50 percent of such earnings from coffee. The collapse of the economic clauses (quota system) of the International Coffee Agreement led to a slump in world prices and in general terms dependence on coffee still continues, especially in producing countries in Africa and Central America and in Colombia.
Coffee growing and its related activities provide a major source of employment in all producing countries. The International Coffee Organisation (ICO) has estimated that coffee growing provides direct full-time employment for 25 million people worldwide. Taking into account related industrial and service activities (processing, marketing, roasting, and transportation) the figure rises to 100 million people, including families.
The magnitude of the impact of coffee on the development of less developed countries may be illustrated by the fact that during the three years of low coffee prices (1989/90 to 1992/3) losses in export earnings are estimated at more than US $ 15 billion. This amount exceeds the total net disbursements of the World Bank (including the IDA) to Africa and Latin America during the same period.
3.2. Post-Harvest Handling and Processing Practices in African Countries.
The following brief descriptions give the type of coffee and the method of processing used in all African coffee growing countries. Annex 4 gives more details for the same countries on:
3.2.1. Angola
Production is almost wholly Robusta and processed by the dry method.
3.2.2. Benin
A small producer of Robusta coffee, which is processed by the dry process,
mostly exported to France.
3.2.3. Burundi
This small country depends mainly on coffee for its export earnings. More
than 90% of the crop is Arabica processed by the wet method on the farms for
final processing at the central hull.
3.2.4. Cameroon
A producer of both Robusta and Arabica coffees, currently in the approximate
ratio of 2:1. The Robusta is processed by the dry method and the Arabica mostly
by the wet process, followed by sun drying.
3.2.5. Central African Republic
Produces mostly Robusta coffee using dry process, for export mainly to
France and Italy.
3.2.6. Congo
Congo produces Robusta coffee by the dry process, again for export mainly
to France and Italy.
3.2.7. Ethiopia
Coffee is the country's most important export. Both the wet and dry methods
of processing are used. Efforts are being made to increase production and improve
quality. Some problems with coffee berry disease occur (see Annex 6).
3.2.8. Gabon
Another small producer of dry processed Robusta. Availability is limited
and most of it is imported by France and The Netherlands.
3.2.9. Ghana
Dry processed Robusta is produced for export to the UK, The Netherlands
and Germany. Quality, usually, is not impressive.
3.2.10. Guinea
This country is mainly a Robusta producer processed by the dry method and
exported to Eastern Europe and former USSR.
3.2.11. Equatorial Guinea
Robusta and small quantity of Arabica are grown and processed by the dry
process.
3.2.12. Ivory Coast
One of the worlds largest producers and grows mainly Robusta which is processed
by the dry method. The coffee is marketed by grade (size of bean) and quality
is generally very uniform.
3.2.13. Kenya
Grows the Arabica species almost exclusively. The wet method of processing
is generally used to produce some of the finest coffee in the world, with excellent
acidity and usually good body (see Annex 5).
3.2.14. Liberia
Produces mainly Robusta coffee, which is processed by the dry method.
3.2.15. Madagascar
Both Arabica and Robusta are grown and processed mainly by the dry method.
Although coffee is the country's most important export, some problems with pests
and diseases have occurred.
3.2.16. Malawi
Malawi produces Arabica coffee, mostly by the wet process. Quality can
be good but production is small and erratic. Some problems with pests and diseases
have occurred.
3.2.17. Nigeria
Robusta and a little Arabica are grown, all processed by the dry process.
Coffee is a minor export of Nigeria and quality is apt to be somewhat irregular.
3.2.18. Rwanda
Arabica coffee is processed by the wet method and is generally sundried.
Quality varies and occasionally can be quite good. Exports have to follow a
long route, usually through Uganda and Kenya.
3.2.19. Sierra Leone
Grows mainly Robusta and processed by the dry method.
3.2.20. Tanzania
Tanzania is a producer of both Arabica and Robusta coffees. The washed
Arabica is of fair quality but can seldom match the best Kenya coffees. There
have been problems with pests and coffee berry disease. A development programme
is under way to improve quality and yield.
3.2.21. Togo
Producer of Robusta processed by the dry method and exported to The Netherlands,
France and Germany.
3.2.22. Uganda
95% is Robusta coffee, which is processed by the dry method. Uganda is
a major African producer and relies heavily on coffee for export earnings. The
quality can be irregular. The USA, UK and Japan are the main buyers; there are
occasional logistical problems in transporting the coffee to Mombasa (Kenya)
which is the main outlet.
3.2.23. Zaire
Over 80% of the crop is Robusta coffee and the remaining is Arabica. The
Robusta is generally dry processed and tends to be of irregular quality; the
Arabica can of very good quality.
3.2.24. Zimbabwe
Cultivation of Arabica, which is processed through the wet method, has
only commenced in the last few decades and quality is good.
3.3. Major Factors Affecting Coffee Quality in Africa.
3.3.1. Agronomic Practices
Agronomic practices are poor in most of coffee growing countries in Africa. Over 80% of coffee from these countries is produced by small-scale farmers who lack adequate education on proper agronomic practices for coffee farming. All these countries which are classified as poor, and luck enough resources to offer effective Agricultural Extension services to their farmers.
In Kenya for example, the Government employs sufficient extension
workers in all the Districts. These extension workers are unable to reach the
Farmers due to several reasons:
· Transport facilities are not adequate/missing.
· Infrastructure is very poor and particularly the roads are in very
bad conditions and most of the time are impassable.
3.3.2. Research and Development linkages
The linkages between the research institutions and farmers is very poor. In Kenya for example, the research linkage to the farmer is the agricultural extension worker who lucks enough resources to reach the farmers. Information technology, which is more modern, faster and easier means of information transfer is almost non-existent in these countries at the level of the farmer.
3.3.3. Method of processing
In most of the African coffee growing countries, the coffee is processed by the dry method. Wet processing is more expensive than the dry method and more care is taken right from harvesting to drying leading to a better quality coffee. Wet method is only used in very few countries in Africa, which include Kenya, Ethiopia, Tanzania etc.
3.3.4. Lack of affordable Credit
Credit to farmers in most African countries is only available from the Commercial Banks, which charge very high interest rates. This limits the farmer's ability to buy farm inputs like fertilisers and chemicals. Hiring of labour when required, like during harvesting is limited.
In Kenya, a project, "The Second Coffee Improvement Project" (SCIP) assisted farmers tremendously between 1993-1998. This was a World Bank/Government of Kenya funded project, which provided subsidised credit to farmers for purchase of farm inputs, improvements of the pulping stations and cash advance for harvesting labour costs. It also provided finance to the Government for training of extension staff involved in coffee extension and training of farmers. The terms of the credit were at 15% interest rates, 1-year grace period and a repayment period of 2 years. The prevailing interest rates in the commercial Banks by then were about 30%.
3.3.5. Problems associated with Wet Processing method (Kenyan example)
3.3.6. Drying
Drying of coffee after pulping (for wet processing) and after harvesting (for dry processing) is a very critical stage in determining the quality of coffee. In these two cases, coffee is dried by either individual farmers or the co-operatives. During cold weather conditions, coffee takes long periods to dry and some will reabsorb moisture. These conditions encourage mould growth, which lead to production of mycotoxins. This problem can be solved by use of mechanical drying instead of sun drying during such weather conditions. However these farmers and societies are poor and cannot afford the mechanical dryers.
3.3.7. Storage
Storage of coffee at farm level and the co-operatives after drying is also a stage, which can affect coffee quality. During wet and dump weather conditions, the coffee can reabsorb moisture, which will lead to loss of quality.
In Kenya for example all co-operatives have coffee stores but are advised to deliver their coffee for hulling immediately after drying. This is not always the case. Due to management problems in these co-operatives, sometimes the coffee stays in stores for very long periods, which compromises on the quality. Some co-operatives have constructed modern stores that are electric fans ventilated but most cannot afford.
3.3.8. High cost of Farm Inputs
In most cases, the cost of farm inputs is very high and most farmers cannot afford. In Kenya, almost all farm inputs for coffee, like fertilisers and chemicals are imported and the cost of importation is passed on to the farmer. These costs include the shipment and government importation tax. This makes the inputs unaffordable to most farmers. Due to this luck of use of the required farm inputs, the eventual coffee quality is compromised.
3.3.9. Transportation / shipment
Transportation of the green coffee from the producing countries to the main consuming countries is normally by sea, which exposes the coffee to warm and humid conditions. Reabsorption of moisture from the air may occur which will encourage mould growth.
3.4. Main Defects of Green Coffee.
3.4.1. Colour defects
3.4.1.1. Black beans
Any bean which is at least half-black on the outside or inside is called a black bean. This is considered to be the main defect of green coffee, and is used as a standard in inspection tests. Recently, however, stinker (see aroma defects), beans have become more common in batches of certain origins, depreciating their value considerably.
Black beans make the beverage taste bitter, disagreeable, and render it generally undrinkable.
The reason for this defect is attributed to prolonged fermentation of cherries picked from the ground, which then undergo a poor drying process with intermittent periods of wetting. The presence of black beans is rare in wet processing, except where the cherry has been harvested from the ground, or if there are still some beans left from previous operations in the fermentation tanks and poorly cleaned washing channels.
3.4.1.2. Greyish or dark grey beans
There are several reasons for this colour: harvesting before the beans are ripe, initial fermentation of cherries in the heap, poor drying or repeated spells of wetting if stored under poor conditions, etc. Beans of this colour are classified as undesirable.
3.4.1.3. Foxy beans
These have red colouring which is essentially due to artificial drying which has been overdone. Reasons for this include high drying temperature, drying period extended over a long time, or the beans not having been sufficiently mixed. It may affect the tissues to varying depths. If the colouring is very superficial, it could be the result of excess fermentation coupled with loose pulp. In some cases it has been attributed to the adherence of a thin film of reddish soil from the drying area during hulling, if the soil has high clay content.
3.4.1.4. Coated or murram-coloured beans
This colouring is imparted to the bean by the presence, either wholly or partially, of the skin. It is a defect of minor importance, except for extremely high quality Arabicas.
3.4.1.5. White, opalescent, and glassy beans
These are generally beans that have been insufficiently dried or have reabsorbed some moisture, within which internal enzyme reactions often appear. These beans are less dense than a healthy bean of the same volume. Glassy beans are the result of artificial drying using too high a temperature at the beginning, resulting in a rapid release of water vapour. They are considered undesirable.
3.4.1.6. Blotchy and spotted beans
Blotchy beans have spots of various colours due to incomplete or irregular drying. Spots appear on the beans due to the effect of oxidising agents, which are present on the surface tissues following injuries. These develop particularly during the preparation of beans, often during hulling, but certain lesions are induced by pest or disease infections.
Poor fermentation or the use of water with a high iron content (formation of black precipitates with the tannin from beans) for wet processing can also give rise to spots. The presence of whitish spots reveals poor drying or the initiation of germination resulting in enzymatic reactions.
3.4.2. Defects in the aroma and taste
3.4.2.1. Stinkers
When these beans are cut, they release a putrid, nauseating odour, which is also rather volatile and this odour will have disappeared after a few hours. As the appearance of these beans is no different or only slightly different from that of healthy beans, it is very difficult to distinguish them. Unfortunately, their bad odour becomes apparent during roasting and the presence of a single stinker in a cylinder is enough to contaminate its entire contents. The taste comes through in the beverage and produces undrinkable coffee.
It has now been established that stinkers are caused either by excessively long fermentation or the use of unclean water. If it is a matter of only a few beans in batch, the reason may be that the fermentation tanks or washing channels have been poorly cleaned and all the beans from the preceding operation were not removed.
3.4.2.2. Rancid or acid beans
These beans have a rather dark brown colour and give off a disagreeable odour when cut. They are the result of poorly managed, excessively long fermentation and their defects are discernible in the beverage.
3.4.2.3. Musty beans
These beans are either partially or totally covered with mould. They give off a characteristic odour, which does not disappear after roasting and is transmitted to the beverage. The presence of a few musty beans in a batch is enough to contaminate the total contents. It is usually the result of incomplete drying, or the re-absorption of moisture in the storage areas or during transport (wet bags).
3.4.2.4. Rio flavoured coffee
A slightly medicinal aroma is characteristic of certain coffees from the regions of Rio and Victoria in Brazil, due to the metabolic activity of bacteria in the soil, which produce an iodised substance which is absorbed by and transported within the coffee tree by the sap. However, it is not always regarded as a defect, as this very specific flavour is appreciated by some consumers, mainly in regions of Northern France.
3.4.3. Other abnormalities
3.4.3.1. Droughted beans
These arise from cherries that have been harvested several weeks before they are ripe. Amongst the many known reasons for the deterioration of the quality of coffee, the high percentage of unripe beans in the batches is a major factor. Farmers should be discouraged from harvesting unripe beans.
3.4.3.2. Broken beans
The beans become broken due to inadequate adjustment of the pulping equipment or hullers, or an excessively rapid rotation of the cylinders during pulping. Breakages most frequently occur during hulling when the coffee is too dry. Broken beans adversely affect the appearance of the batch, but more importantly they roast faster than whole beans, and tend to become charred. Their presence therefore has a negative effect on the quality of the beverage.
3.4.3.3. Crushed beans
These are rather flat beans, the median furrow of which has been laid open. Unlike broken beans, crushed beans are the result of processing insufficiently dried coffee.
3.4.3.4. Pitted beans
The surface of beans which have been infested by insects are more or less riddled with small, round holes such as those produced by the berry borer. Cutting them open reveals the pores bored by the insect.
3.4.3.5. Elephant beans
These are large, deformed beans, consisting of several embryos enveloping the endosperm. Within a batch, they upset the uniformity of the bean size and are also a problem during roasting.
3.4.3.6. Foreign matter
Whatever the precautions taken during harvesting and preparation of coffee, the batches are rarely completely free of foreign matter. Mostly encountered is: soil and dust (transported by the wind during drying); small stones (careless harvesting, drying on packed earth); pulp (poorly executed pulping) or parchment debris (incorrect adjustment of the huller's fan) Sometimes the beans are still in parchment (faulty huller operation) or dry cherries are present (great variation in the size of the cherry, huller poorly adjusted). Twigs and pieces of branches are also common.
The presence of soil and other related debris is revealed by handling the beans and observing the marks that they leave on the skin. It is easy to eliminate these impurities by passing the beans through a winnowing machine.
Pulp debris (skins) depreciates the value of the coffee, especially Arabica. The skins resemble large, dark brown fragments and give the beverage a bad taste.
Parchment debris are mostly small and very fragmented and eliminated by use of a winnowing machine or a Catador (see density sorting, 5.11).
Presence of whole parchment coffee beans or whole dry cherries is considered as a major defect because they give the green coffee a disagreeable appearance and are harmful to the roasting process.
Impurities such as twigs, leaf debris and wood fragments are very rarely found in well-prepared coffees. Also, their presence is often indicative, not only of a poorly executed harvest, but also of inefficient processing procedures.
Acid : acidulous taste
Pungent/acrid : sharp, unpleasant acidity
Tart : unpleasant acidity, like sour milk
Alcoholic : taste of distillation tailings
Bitter : sensation in the back of the throat
Astringent : like an unripe cherry
Burned : burnt taste
Body : duration of sensation in the mouth
Harsh : bitter + astringent + green, opposite to soft
Fermented : taste of rotten cherry, similar to alcoholic
Rank : nauseating
Fruity : taste of fruit, sometimes unpleasant and inappropriate
Foxy : Light-brown coloured
Grassy : taste of mown grass
Woody : taste of wood
Mouldy : mouldy taste, musty odour
Potato taste : taste of raw potato
Stinker : nauseating, sickening
Rancid : taste of rancid butter, old oxidised oil
Rummy : taste of rum distillation tailings
Sour : Unpleasant acidity and green taste
Earthy : soil taste
Green : taste of herbal tea
