ITDG 
Interdev Agroalimentaire  

Small-scale processing of coffee (Coffea species)

	Type de fiche	Techniques/Technologies
	Mise en œuvre	ITDG(Royaume Uni)
	
	Zone géographique	; 
	Mots clés	SECHAGE; CAFE; BOISSON; GRILLAGE

	Echelle d’action	Groupe

Contexte
Coffee is the bean of a shrub or tree.  It is processed into a fine dark brown powder that is used as a beverage.  The coffee powder is brewed with boiling water and is consumed as a beverage, often with milk and sugar.  The beans are often sold whole and ground by the consumer as required.

There are several types of coffee bean that differ in taste and colour.  This is due to differences in variety and the climatic conditions under which they are grown. For example:

  Coffea arabica is a glossy leaved shrub or tree with fragrant white flowers.  It grows well in high cool climates (600-2000m above sea level and 15-20 C). Arabica coffee usually receives a premium for its superior flavour and aroma.  
  Robusta coffee comes from the Coffea canephora family.  In general, these plants are found in hotter lowland areas (below 900m above sea level and over 20 C. Robusta coffee is preferred for the production of instant coffee due to higher extraction of soluble solids.
  Liberica (Coffea liberica) is a tree with large leaves and berries that can tolerate hot and wet conditions.  The coffee produced is bitter. It is the preferred type in Malaysia and West Asia.

Coffee beans undergo a fairly complex process of preservation.  They are sun-dried, which removes water from the beans and preserves them by preventing microbial, enzymic and chemical reactions.  Roasting causes a further loss of water and also develops the characteristic coffee flavour.

Problématique / Objectifs
  Harvesting at the correct stage of ripeness is crucial to the quality of the coffee. Coffee cherries are often harvested before they are ripe as the farmers are afraid of theft. Under-ripe cherries are very difficult to process and are of inferior quality.  Over-ripe cherries are not good as they will start to ferment, which causes a deterioration in flavour.
  The cherries should be harvested when they are bright red all over. At this stage the bean can be squeezed out from the pulp by applying light pressure between the finger and thumb.
  The quality of the product is in part determined by the variety of coffee beans that is used.  Some are darker and more bitter than others.
  The quality of coffee depends mostly on its colour and aroma. Both characteristics are developed during the roasting stage and this should be carefully monitored and controlled.  Experience and skill are needed to produce a good quality product.
  There are two main ways of processing coffee _ dry (natural) processing and wet (fermented and washed) processing.  In most cases wet processing is regarded as producing a higher quality product.  However, some areas prefer dry processing for its fuller flavour. Dry processing is the simpler of the two methods and is used in Brazil to process Robusta coffee and in Sri Lanka to process Arabica coffee.

Description/Mise en oeuvre
There are two methods of processing coffee _ dry processing and wet processing.  Dry processing is the simpler of the two.
 
Dry processing
  Harvest fruit
  Dry
  Dehusk
  Clean

Wet processing
  Harvest fruit
  Ferment pulp
  Separate pulp and wash
  Sort
  Dry
  Dehusk
  Dry
  Store
  Roast and cool
  Sort
  Mill
  Pack and store

Dry processing

Harvest fruit
Coffee berries should be harvested when they are fully ripened _ when the berries are bright red and the bean can easily be squeezed out of the pulp. Remove and discard unripe and mouldy or damaged fruit.

Dry
The cherries are dried immediately after harvest.  Care must be taken to ensure that the cherries do not start to ferment during drying. A range of suitable driers are available for drying coffee.

De-hull
After drying the coffee cherries are de-hulled, ie the outer pericarp is removed, to reveal the coffee bean.

Clean
The hulled coffee beans are winnowed to remove the pieces of dry pericarp.

Wet processing

Harvest fruit and sort
Coffee berries should be harvested when they are fully ripened _ when the berries are bright red and the bean can easily be squeezed out of the pulp. Remove and discard unripe and mouldy or damaged fruit.  Immature fruits are green and hard and are very difficult to pulp.

Ferment pulp
The coffee cherries are piled in heaps or placed in woven baskets to allow the pulp to ferment and drain away over several days. The pulp is made of pectic substances, hemicelluloses and sugars and is insoluble in water. During fermentation the enzymes in the pulp, together with bacteria and yeasts, break down the pulp, which is then washed off.

Separate pulp and wash
The pulp (which is white in colour) and the outer red skin that surround the bean are removed and the bean separated.  For small-scale units, the cherries can be pulped using a mortar and pestle, however, this is very labour intensive.  Small-scale pulping machines are available and should be used.

The two common types of pulper are a drum pulper and a disc pulper.  A drum pulper involves a rotating drum with a punched sheet surface and adjustable breast plate between which the cherries are pulped and the beans and pulp separated. The distance between the drum and the breast plate has to be adjusted so that the pulp is remove without the beans being damaged. A disc pulper separates the bean from the pulp by rubbing the beans against a roughened surface.

Sort
After removing the pulp, the beans are sorted and the healthy, undamaged beans are selected for drying.

Dry
Beans are dried in the sun for 5-6 days or, using artificial driers, until the moisture content reaches 10%.  They should be dried slowly to prevent cracking, but not too slowly as this allows the growth of mould.

Dehull
The dried beans are left to stand for about 8 hours in a well ventilated place, then the outer skins are removed by gentle rubbing.  Winnow to remove the dry skins.

Dry
Dry again in the sun for 5-6 days.

Store
Store in sacks in a cool dry place until used.

Roast
Roast at about 200-250 C for 10-15 minutes. An experienced processor will be able to judge by eye when the beans are fully roasted.  Cool to room temperature.

Sort
Remove the burned beans and recycle the under-roasted beans to be re-roasted.

Mill
The beans can be ground into a fine powder.  However, because of the strong consumer distrust of ground products, it is probably better to sell the whole beans.  Whole beans also retain their taste and aroma for longer than the ground material.

Pack and store
Whole beans or the powder are stored in airtight containers and stored in a cool dry place. Milled beans should be packaged quickly as the volatile aromas will be quickly lost. The powder should be stored in airtight and moisture-proof containers such as jars, cans or composite plastic bags. Polythene is not a suitable material for this product because of its low barrier to moisture and air, leading to a loss of aroma and moisture pick-up after a few days.

Résultats/Eléments chiffrés
The following equipment is required:

Pulper (optional) or mortar and pestle
Plastic bins for fermentation
Drier
Roaster
Dehuller (optional)

Enseignements
  Processors should pay strict attention to hygiene.  During drying (if sun-dried) the coffee cherries should be protected from dust and dirt. Animals, rodents and birds should be kept away from the cherries during drying as they are a potential source of contamination. 
  The traditional method is to lay the cherries on a clean dry floor and dry in the sun.  The bed depth should be less than 40mm and the cherries should be raked frequently to prevent fermentation or discoloration.  Sun drying is not the preferred method as it is prone to a range of problems _ contamination with dirt or dust; wetting and subsequent damage caused by rain showers and heft of the drying cherries.
  Solar cabinet driers are suitable for use in the dry season.  The drier should be ready as early in the morning as possible, so as to benefit from the maximum hours of sunlight. The coffee beans should be stirred regularly to ensure even drying rates and a uniform colour is achieved. At night the crop should be removed from the drier and placed in a cool dry room.
  During the rainy season, it is preferable to use a mechanical drier.  The solar drier will keep the coffee beans dry, but the lack of sunlight will prolong the drying period and may lead to the growth of mould on the beans.
  Roasting is important to the final flavour and aroma of the coffee.  It is a time and temperature dependent process and varies widely according to personal choice and taste. The degree of roast is assessed visually. One method is to watch the white line that separates the two sides of the bean. When the line starts to turn brown, the bean is ready. The beans can be roasted in a saucepan as long as they are stirred continually. Roasting in sand improves the process as it provides a more even heat.  Using a small roaster produces a higher quality product.
  Roasted beans can be stored in sacks for many months in a cool, dry store.  Milled beans should be packaged quickly as the volatile aromas are soon lost.  The powder should be packaged in air-tight jars and stored in a cool, dry place.  It has a short shelf life.  Once opened the flavour deteriorates rapidly.

Auteur : Sue Azam Ali
Saisie le : 19/03/2002 

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