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  • QA 150
    Question:
    For robusta, is there any difference in yield between dry and wet processing?
    Background:
    What is the yield by weight for robusta coffee by wet processing as opposed to dry processing?
    Asked by:
    Extension Agent/Researcher - Panama
    Answer:

    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

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