Page 10 - Vol.38-No.1

CROP PROTECTION

COFFEE PROCESSED WET OR DRY

dry, but water plays an important part ty (taste, flavour and aroma) of Robusta
in the first stages of processing at least coffee is not generally considered to
for some coffee origins. be sufficient to warrant use of the wet
Commercially-grown coffee is gen- method. Dry processing involves en-
erally one of two types – Robusta or forced drying of picked coffee berries
Arabica. Coffea robusta is usually grown in the sun (or artificially) to produce
in the lowland tropics and has a high- dry coffee cherry. This is cleaned and
DR. TERRY MABBETT er caffeine content (2.0 %), which is hulled to remove the husk (dried pulp
and integument) from the bean.
reckoned to afford significant protec-
Cupped coffee is an infusion of many tion against insect pests and diseas- Mechanics of wet
different chemicals made by mixing es. Coffee arabica, with a lower (1.0 %)
boiling hot water with the roasted re- caffeine content and less tolerance processing
mains of coffee beans, the seeds of of insect pests and diseases, is more Wet processing entails the following
the coffee tree (Coffea sp). Prominent discerning of growing conditions. Ar- steps:
amongst them is caffeine, a stimu- abica bushes tend to thrive at higher • Sorting and cleaning – even after
lant, which gives mainstream coffee altitudes where the air and water are careful harvesting of ripe coffee there
drinkers the much sought after and cleaner and purer, temperatures are will still remain a number immature
valued ‘kick start’ or stimulus to their moderated and pests and diseases less coffee berries together with stones and
metabolism. And coffee contains a prevalent. soil. These are removed by a separa-
huge range of additional chemicals Robusta coffee is considered to be tion operation which uses a series of
occurring in specific concentrations inferior in taste, flavour and aroma, sieves.
and combinations to give each coffee compared with Arabica coffee. It tends • Pulping – carried out by a machine
origin (type) its own distinctive taste, to be used for making soluble coffee operation in which the cherries are
aroma and flavour. products sold as powder or granules pressed between fixed and moving
and for ‘instant’ mixing with water. surfaces to remove the soft outer tis-
On the other hand, Arabica coffee is sue (the pulp). Distance between the
reserved for making the percolated moving surfaces is constantly adapted
product, and is therefore marketed as to avoid damaging the beans. Beans
whole dry beans, which are ground be- still enclosed in their parchment are
fore treatment with steaming hot water. separated from the unwanted residue
Because of a perceived higher quality using screening machines and from
and greater potential for taste, flavour where the beans are passed to water
and aroma, the Arabica coffee bean channels where the final separation is
tends to be treated differently during carried out by ‘flotation’, although a
initial stages of on-farm processing. small amount of pulp will remain at-
Small-scale, wet processing of coffee Immediately after picking, the red tached to the beans.
in Tanzania (Picture courtesy Omex ripe cherry (berries containing the • Fermentation - final traces of pulp
Agrifluids)
beans) undergo a pulping, washing are removed by fermentation in which
and soaking procedure using clean the beans are placed in large fermen-
Some coffee chemicals like caffeine cold water, which leads to partial fer- tation tanks so that any unwanted res-
remain unaltered from their natural mentation of the bean. This is sufficient
state in the fresh and living coffee bean. to bring out an ‘early’ chemistry in the
Others develop during processing from Arabica coffee bean and to ‘lay down’
naturally occurring precursors that un- the basis for a favourable taste, flavour
dergo chemical changes, during ‘wet and aroma profile. This is consolidated
processing’ on the farm or later at the during roasting to give a claimed su-
factory during roasting. periority over Robusta in the cupped
All have one thing in common. They coffee infusion.
are soluble in water. Natural coffee ‘Wet processing’ of coffee produces
chemicals must be soluble in water ‘washed’ Arabica beans and which are
to exist and to move in solution in the considered to be the premium in the
living coffee tree and its constituent world of coffee. In some countries such
parts (e.g. coffee berries and beans). as Brazil, Arabica beans do not receive
And cupped coffee chemicals have the washing and soaking treatment,
to be soluble in water to contribute and are therefore termed ‘unwashed’
to taste, aroma and flavour and in the Arabica. These, like most all of the Ro-
case of caffeine metabolic stimulation. busta coffee produced worldwide, are
The final coffee product – dry roasted processed on the coffee estate by the
beans for ‘real’ or percolated coffee or ‘dry’ processing method. Red-ripe coffee cherries of Coffea
coffee granules and powder to prepare robusta, ready for harvest and on-farm
soluble (instant) coffee – may well be Wet processing is much more expen- processing (Picture Dr Terry Mabbett)
sive than dry processing and the quali-

8 Vol. 38 No. 1