• QA 152
    How can cherry be pulped manually?
    We would like to know if traditional but efficient systems exist for the manual pulping of coffee cherries. If so, which?
    Asked by:
    Farmers institution - Gabon

    As far as we know Gabon is a robusta producing country. Our answer is therefore based on the assumption that your question is related to the processing of robusta.

    Manually operated drum pulpers are the best-known and most efficient traditional method, found particularly in East and Central Africa. Pounding or 'pilonnage' of cherry as sometimes practised greatly damages the bean and is not recommended.

    Pulping of cherry greatly reduces the mass of material to be dried. This was the primary reason why pulping systems were introduced, particularly for use on robusta coffee grown in areas with high temperatures, humidity and rainfall that made drying of large quantities difficult. However, the process normally includes washing and/or fermentation to remove the sticky mucilage that adheres to the parchment bean. In robusta the mucilage is thicker and stickier than arabica, making it more difficult to remove. Usually therefore a robusta producer needs to engage in the entire process, so including washing and fermentation. This is difficult for individual smallholders who may produce small quantities only and cannot afford the necessary facilities.

    NB: See topic 11.01.01 and 11.01.02 of the Guide for more on dry and wet processing.

    The drum pulper consists of a small rotating drum with a punched sheet surface and an adjustable metal breastplate between which the cherries are pulped. Cherries are fed into pulping channels through a small hopper. When turning the handle the descending cherries are pulped by increasing friction as the distance between the surface and the ribs on the breastplate narrows. To pulp cherry of uneven size strips of flexible rubber are used instead of metal ribs. Depending on circumstances, throughput is in the region of 300 kg red-ripe cherry per hour when operated manually, and around 600 kg when motorised. It is also possible to increase throughput by linking the unit to a treadle or to a bicycle that is pedalled whilst on a stand. After pulping the coffee will be washed by hand to remove as much of the mucilage as possible and is put out to dry. Single disc pulpers are another option.  These use a vertical disc instead of a drum but the principle is the same. For optimal efficacy the discs should be re-sprayed (re-metallised) every two years.

    We would caution however that hand pulpers are generally used for arabica processing. Robusta is either entirely dry processed, i.e. the traditional method that produces 'natural robustas'; or it is entirely wet processed so including washing and (natural or mechanical) fermentation. Simply pulping cherry and then drying it will produce a different, a third product…

    Q&A 008 in the Archive deals with exactly this question for Brazilian arabica where 'pulped naturals' are a relatively new product. Cherry is pulped and immediately dried with the mucilage adhering to it. To note though that the first stage in drying, i.e. to where the mucilage no longer sticks to the hand, is critical. It requires very close supervision and very frequent turning of the thinly spread parchment, as well as clear sunny skies with low humidity.

    The question is whether 'pulped robusta', i.e. neither 'natural' nor 'wet processed', would easily find a market, especially if the end-product was not homogeneous which is likely if it originated from numerous individual smallholders using hand pulpers.

    Our recommendation therefore is twofold:

    • Undertake trials by importing one or two drum pulpers and testing the coffee's appeal;
    • Simultaneously investigate what the possibilities are to produce wet processed robusta of a quality and quantity that might attract commercial interest, particularly in the specialty cum espresso market segment.

    We also recommend reading section 11.09 of the Guide, particularly topic 11.09.02 that discusses wet processing using small mechanical units that remove both pulp and mucilage in a single operation. You may also be able to obtain more information by visiting www.cirad.fr.

    Potential suppliers of manual and motorised units include:

    Brazil: www.pinhalense.com.br.
    Colombia: www.penagos.com.  
    India: www.mckinnon.co.in  
    United Kingdom:  www.johngordon.co.uk. - www.alvanblanch.co.uk

    Posted 31 May 2007


    Related chapter(s):
    Related Q & A:
    Q&A 008, 053, 150