Primary Processing
A) General information – Fruit to FAQ
The ripe coffee fruits (cherries) go through a number of operations aimed at extracting the beans from their covering of pulp, mucilage, parchment and film to improve their appearance. The resulting clean coffee (FAQ) can then be roasted and ground to obtain the coffee powder which is fit for human consumption. There are two main techniques used to obtain the clean coffee;
1. Wet processing in
which the fruit is processed in three stages:
• Removal of pulp and mucilage followed by washing to obtain clean wet
parchment
• Drying of the parchment coffee
• Removal of the parchment and film through hulling followed by grading to
obtain the desired grades (sizes) of the clean coffee.
2. Dry processing
which involves two stages:
• Drying of the cherries (usually under the sun) and
• Removal of the dried coverings (husks) in a mechanical operation (hulling).
Wet processing is done for the choice Arabica coffees produced at high
altitudes (over 1,500 m above sea level) in the Mount Elgon areas in the East,
the Highland areas of Nebbi in the North and the mountainous areas of Kisoro
and Rukungiri in the Southwest. The coffees so produced are generally described
as ‘mild’.
Dry processing produces coffees that are described as ‘hard’. These are mainly the Robustas grown around the lake Victoria basin and they account for about 85 % of Uganda’s total annual production. The wet processed (washed) coffees are generally superior to the dry processed in terms of physical appearance and the cup taste.
B) Wet processing:
1. Cherry separation:
The harvest often includes unripe, immature cherries, dried cherries, twigs and
leaves. These are lighter than the mature ripe cherries and can therefore be
removed by a floatation process which can be done in a simple vat or
mechanically in a washer separator, which floats off the undesired impurities
and also washes the ripe cherries.
2. Pulping:
The cleaned cherries are then pulped – a process in which the wet beans are
squeezed out from the cherries leaving the pulp. Pulping can be done using a
hand-pulper with a capacity of about 300 Kg/hr of fresh cherries. The capacity
may be increased by the incorporation of an electric motor or a diesel/petrol
engine. Larger units of up to 4.0 T/hr are available at central pulping
stations. The wet parchment beans have a mucilage layer around them that is
removed by bio-chemical enzyme activity through controlled fermentation to give
‘fully washed’ coffees.
If the mucilage is mechanically removed the coffees produced are referred to as semi-washed.
3. Washing:
After the mucilage is degraded it is removed by washing in a washing channel or
vat filled with water. The density of the parchment coffee is slightly higher
than the water and the beans will sink to the bottom of the vat. It is
therefore necessary to continuously stir the beans using rotary stirring rods
or manually using spades in the washing channel.
In a mechanical mucilage remover, mucilage degradation and washing are done in a single operation.
4. Drying:
The wet parchment free of mucilage at moisture contents of 50 – 60 % is then
dried on suitable raised drying tables to the required 12 % to ensure their
conservation. Mechanical driers to hasten the drying regime can be used after
draining off some of the water.
C) Dry Processing:
1. Harvesting:
The harvested cherries are usually not sorted before commencement of the drying
regime. Careful harvesting to exclude immature cherries and extraneous matter
e.g. stones is essential.
2. Drying:
The drying regime should begin immediately after harvest to avoid the
development of undesirable taints and moulds. The cherries are spread out to
dry in the sun on suitable drying surfaces e.g. raised trays or tarpaulins. The
coffee must be frequently stirred to achieve uniform drying. The coffee should
not be rewetted at any time during the drying regime.
Drying will be complete when the dried cherries (kiboko) have attained moisture content of 13 – 14 %.
D) Hulling:
In the wet method the dried coffee beans have a parchment covering while in the
dry method, the beans are covered with the husk. These are removed in a
mechanical operation known as hulling. The hullers usually rotate at a speed of
450 – 800 rpm. Higher speeds result into a polished appearance but also
increase the breakages. There are about 250 active hulleries now operating
throughout the country.
The resulting clean dry coffee beans are in both cases referred to as FAQ (Fair Average Quality). The FAQ is then sorted according to size using perforated sieves and by specific gravity in a gravity table or by pneumatic sorting in a catador.
Secondary Processing
FAQ to green Export coffee:
Over 95 % of the total annual coffee production is exported as green beans. Secondary processing also known as export grading transforms the clean coffee (FAQ) into the various coffee grades that meet the international standards. The process involves cleaning the FAQ, drying the coffee if wet (M.C over 13 %) followed by size grading using perforated screens of the desired size. The sorted beans are the gravimetrically sorted to have uniform specific density before bagging off and loaded into containers for transportation to the ports.
Currently, there are about 19 active export grading factories, four of these are located in the Bugisu region, one is located in Mbarara town in the Western region and the rest are in Kampala.
1. Pre-cleaning and
de-stoning:
The FAQ coffee collected from the various suppliers is of mixed quality
depending on the individual suppliers storage and handling techniques. The
coffee is often wet (M.C > 14 %) and includes extraneous matter e.g. stones,
chaff etc. The FAQ passes to the pre-cleaner where the undesirable impurities
that are often lighter than the good beans are removed. The wet FAQ passes to a
drier. Dry coffee then continues to a destoner where the denser stones are
eliminated.
2. Size grading:
The cleaned coffee then passes to a grader, which often consists of a box
fitted with screens of various sizes in descending order. The larger beans are
retained on the required screen and pass to a lateral exit.
3. Gravimetric
sorting:
Although the sorted beans are now of the same size, they may vary in weight
mainly due to poor agronomic practices especially the harvesting of immature
cherries. The coffee passes over a gravity table where separation occurs at
various points on the fluidized bed.
4. Bag-off:
The coffee is then bagged in jute bags of 60 Kg which are then loaded into a
container for transportation to the port.
The following are the Ugandan export grades:
Arabica
Robusta
Washed Natural
Washed Natural
1. Bugisu AA Drugar A Screen 1900 Wur
A
B 1800
PB
C 1700
B
1600
C
1500
E
1400
2. Wugar A
B
C
Drugar = Natural Dry
Uganda Arabica
Wugar = Washed Uganda Arabica (other than Bugisus)
Wur = Washed Uganda Robusta.
Other improved grades for the niche markets include Organic and Specialty coffees.
Tertiary Processing
Green coffee to the cup:
The domestic coffee
consumption is still very low at about 3 – 5 % of Uganda’s total annual
production. There are various reasons for this namely;
1. Low promotion on the domestic market to combat the traditional misgivings
against coffee consumption
2. The domestic roasters face fierce competition for the good graded coffee,
which can be exported for higher revenues. The roasters thus resort to cheap,
lesser quality coffee e.g. rejects and BHP, which do not give a very palatable
powder.
3. Inadequate roasting equipment and packaging materials.
At the moment there are only about 12 registered domestic roasters. Three of these are located in the eastern Bugisu area of Mt Elgon and process Arabica coffees. Two roasters are processing their coffee at the TANICA soluble coffee factory in Bukoba, Tanzania and then re-packaging the powder in Kampala before distributing to the local and regional markets.
However several new coffee shops have began operating and these have continued to attract a sizable middle class clientele
