Coffee : small-scale processing
Practical Action
These can be manually operated but larger
scale units are normally fitted with a motor.
Disc pulpers
The same concept is involved with the disc
pulper except that the pulp is removed using
abrasion by a rough disc.
Mucilage removal The amorphous gel of
mucilage around the bean consists of
hemicelluloses, pectic substances and
sugars and is insoluble in water. This
mucilage can be removed by chemical
methods or warm water but, for small-scale
units, the only feasible method is
fermentation. Fermentation involves the
beans being placed in plastic buckets or
tanks and left until the mucilage has been
Figure 3 : Separation of pulp and beans
broken down by natural enzymes and
bacteria. The coffee should be stirred occasionally and every so often a handful of beans
should be tested by washing them in water. If the mucilage can be washed off and the beans
feel gritty rather than slippery, the beans are ready.
Drying The beans should then be washed and dried immediately to prevent spoilage and
the development of off-flavours. To prevent cracking the coffee beans should be dried slowly
to 10% moisture content (calculated on a wet-basis) using the same drying methods
described above.
Hulling and cleaning After drying the coffee should be rested for 8 hours in a well
ventilated place. The thin parchment around the coffee is removed either by hand, in a
pestle and mortar or in a small huller. The hulled coffee is cleaned by winnowing.
Roasting and Grading
The final flavour of the coffee is heavily dependant on how the beans are roasted. Roasting is
a time- and temperature-dependant process. The roasting temperature needs to be about
200ºC.
The degree of roast is usually assessed visually. One method is to watch the thin white line
between the two sides of the bean, when this starts to go brown the coffee is ready. As
preferences vary considerably from region to region, the locally-acceptable degree of roast will
need to be assessed.
Coffee beans can be roasted in a saucepan as long as they are continually stirred. A small
improvement is made by roasting the coffee in sand, as this provides a more even heat.
A roaster will produce a higher quality product. The simplest roaster is basically a tin can
with a handle so that it can be rotated slowly over a fire. There are various other roasters
suitable for larger scale units.
Coffee is graded by size, shape, odour, density and colour.
Grinding
It is easy to assess the quality of whole coffee beans. However, ground coffee beans produce
a brown powder which can be easily adulterated. Because of this there is often market
resistance to ground coffee. This market resistance can only be overcome by consistently
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