All things being equal there should be no difference but in
practice there always is…
The original reason to wet process robusta was to reduce
the volume of coffee that needed to be dried. Accompanying
advantages are relatively easy separation of under/overripe cherry
and faster drying. However, provided it is correctly processed,
'pulped and washed robusta' also nearly always has a more neutral,
milder cup. Over time this has brought it to the attention of the
specialty coffee industry, particularly of course the espresso
segment, and we assume your question is posed with this in
mind.
To achieve quality pulped and washed robusta only fully
ripe cherry should be harvested and careful attention must be paid
to the entire process. The wet processing of robusta is
riskier and more difficult because the mucilage is thicker and
stickier than it is in arabica. In some cases fermentation may not
be complete even after 72 hours which is too long. And, considering
the high temperatures and low altitude at which robusta is usually
grown, the process requires extremely careful monitoring to avoid
over-fermentation. However, the development of smaller motorised
processing units or eco-pulpers, combining depulping and frictional
mucilage removal with minimal water use, today enables also small
growers to benefit from the growing demand for wet processed
robusta.
To answer your question directly the
following:
If all factors are exactly equal (degree of cherry ripeness,
moisture content etc) then there is no notable difference in the
clean coffee yield between dry and wet processed robusta.
However, for wet processing the harvesting of fully ripe
cherry also means larger beans without most of the immatures and
other rejects that are otherwise present. This in turn means a
better conversion from cherry to clean bean. The ratio cherry-clean
bean of course also depends on the efficiency of the process
itself, the moisture content to which the coffee is dried, and the
percentage of rejects that may be removed during processing.
The ratio cherry-clean bean varies from country to country,
and from plantation to plantation. As such we cannot give any
precise figures other than to say it can range from 5 (good) to as
much as 7 (poor) kgs cherry to 1 kg clean bean.
If there are serious prospects for the commercial wet processing
of robusta in Panama then we would recommend to visit www.penajos.com. and www.pinhalense.com.br for
more information and, possibly, to arrange trials using small or
eco-pulpers..
Posted 22 May 2007