Coffee : small-scale processing
Practical Action
Solar drying
Figures 1 and 2 are designs for two
solar driers - the solar cabinet drier
and the Exell solar drier. The coffee
should be placed in the trays in the
solar drier no deeper than 3 cm and it
is better if the whole tray area is
covered.
Figure 1 : The solar cabinet drier
The drier should be filled with coffee
as early in the day as possible so that all possible sunlight hours are used. The coffee should
be stirred regularly so that a uniform colouration is formed. At night, the crop should be
transferred to a cool dry room to prevent moisture condensing on the coffee.
Artificial driers
In the wet season solar drying of produce
is difficult and alternative driers are
necessary.
Hulling The dried cherry is then hulled
to remove the pericarp. This can be done
by hand using a pestle and mortar or in a
mechanical huller. The mechanical
hullers usually consist of a steel screw, the
pitch of which increases (and therefore the
pressure) as it approaches the outlet so
removing the pericarp.
Cleaning The hulled coffee is cleaned
by winnowing.
Wet processing In this method the
cherry is squeezed in a pulping machine or
pestle and mortar which removes the outer
fleshy material (mesocarp and exocarp)
leaving a bean covered in mucilage. This
mucilage is fermented and dispersed. The
bean is then washed and dried.
Figure 2 : The exell solar drier
Pulping This involves the removal of the outer red skin (exocarp) and the white fleshy pulp
(mesocarp) and the separation of the beans from the pulp. Immature cherries are hard and
green and very difficult to pulp. If the coffee is to be wet-processed, correct harvesting is
essential. The two most common pulpers most suitable for small-scale units are the drum and
the disc pulpers.
Drum pulpers (Figure 3)
This pulper comprises a rotating drum with a punched sheet surface and adjustable breast
plate between which the coffee cherries are pulped. The pulp and the beans are then
separated using a simple gravity system. The distance between the drum and the breast plate
has to be adjusted so that the pulp is removed without the beans being damaged.
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