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  • QA 187
    Question:
    Why separate coffee beans by size during milling and then mix them again for export?
    Background:
    I have been visiting some of the large coffee mills in East Africa where I observed very detailed grading systems that separate coffee beans by size. But at the same time I'm told that most exports consist of mixtures or blends? I would like to know why this is so?
    Asked by:
    Research/extension - D.R. of Congo
    Answer:

    Coffee mills routinely separate coffee beans by size, mainly because of final processing and quality considerations. The number of size grades actually exported depends on what individual countries or exporters apply.

    Generally speaking, size grading ahead of final export preparation facilitates the separation of heavy and light beans; makes it easier to remove very small beans, broken beans and shells; and helps reduce the incidence of insect damaged beans and other defectives.  This is so because final processing equipment such as catadors, gravity tables and sorting machines always works better on relatively evenly sized beans.  To note also that large and small beans do not roast well together. *

    The degree of separation (number of size grades) depends on the final objective.

    If done purely to streamline processing and produce bulk exports then it would suffice to separate out beans over a certain size (over-sized beans for example), and the smallest beans. This then leaves the bulk of the product to be processed as a single grade, the bean size of which varies within an accepted range.

    If however larger and medium sized beans realise better prices separately as opposed to being left in the bulk, then of course this warrants the production of multiple export grades by size.

    Most East African coffee mills habitually produce a number of grades, first separated by bean size and then further defined by quality (taste). The main reason is that high quality arabica size grades realise better prices when sold separately, particularly for the whole bean market where the end-user sees the actual beans.  Nevertheless blending before final export, also of size grades, often takes place for a number of reasons…

    • Exporters may combine small individual lots of the same size grade that are of comparable quality to arrive at an exportable parcel. But not all whole bean buyers insist on just the largest bean size and may be satisfied by a mixture of, for example, the largest beans and the next size down, as long as the end result produces the same quality (taste result).
    • For high quality coffee that is not destined to be retailed as whole bean exporters may combine a number of size grades. The mixture may look somewhat uneven from the size perspective but is acceptable as long as it produces the required quality.
    • Not all coffee merits the same degree of final processing. However, mills do not change their processing arrangements each time a different parcel of coffee comes in from an individual grower. So, not all size grades from all suppliers merit marketing separately but they are produced as a matter of course. Exporters then blend different coffees and grades to create larger (usually multiple container) sized parcels that satisfy particular markets.

    To summarize…

    • One reason coffee is size graded is to facilitate final processing, and to avoid problems with roasting. Large and small (or heavy and light) beans do not roast well together.
    • At the top of the quality scale different bean sizes, particularly larger beans, are mostly exported separately because in this way they fetch better prices. Even so, an export parcel may be a blend of different but compatible coffees.
    • Most medium and small beans are retailed as roast and ground (R&G). So, for export they are often blended into larger parcels (depending on quality and provided the mixture is not so uneven as to present problems during roasting).

    One should remember that 85 to perhaps 90% of the coffee consumed in the world is of average or mainstream quality, sold into a market that is dominated by a number of very large multi-national roasting companies. Roasting large amounts of green coffee on a daily basis requires a constant supply of standard quality coffees, supplied in substantial, yet homogeneous parcels. Blending different grades and qualities together enables also smaller producers to supply shipments that meet mainstream requirements, both in terms of quality and minimum acceptable tonnage. At the same time, growers in East Africa are retaining the ability to separate and market their top quality and top grades individually… **

    *   Small and light beans tend to over-roast during the time it takes to roast larger and heavier beans. Roasters therefore strictly limit the proportion of small and light beans, if any, they will tolerate in whole bean coffee. Coffee processing and processing equipment are discussed in Chapter 11 (Coffee quality) of the Guide, particularly section 11.05.

    **  See topic 03.01.10 for more on the meaning of mainstream quality and the difference between it and specialty coffee. See section 11.08 on quality in relation to the 'mainstream business'.

    Posted 01 April 2008

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