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  • Causes of poor colour

     
     
    Dullish and sometimes brownish greens often result from (too rapid) mechanical drying which also tends to flatten the liquor quality. Uneven colour is usually a consequence of poor drying techniques.

    Uneven, mottled greens, often with mottled, blotchy, whitish or soapy beans, suggest the coffee was spread too thickly when drying, that it was not turned often enough, or that it was dried too rapidly. Such beans subsequently show up as mottled beans (also called quakers by some) in the roast.

    Mechanical drying is often used if the climate or the tonnage to be handled do not allow one to depend entirely on sun drying, that is, if the weather is too unreliable during the harvest season, or the quantities of cherry to be handled are simply too big. For washed robusta it is also a means of avoiding (secondary) fermentation. Collectors (those who buy parchment or dried coffee in cherry from small farmers) often use mechanical drying to bring the moisture content down to acceptable levels. Subsequent storage or conditioning in bulk bins with airflow capability then evens out the moisture content throughout the entire parcel or stack.

    Brownish tinges in arabica greens can result from the harvesting of overripe cherries, or from allowing too many skins to enter the fermentation tanks. The use of dirty water, under-fermentation, insufficient washing after natural fermentation, or the mechanical removal of mucilage are other contributing causes. In washed arabicas foxy beans (where the silver-skin has turned reddish-brown) are usually due to the harvesting of overripe cherry, or keeping cherry overnight before pulping.

    Fading is an indication of problems. A generally bleached or fading colour suggests that the coffee is ageing, or that it was over-dried, especially so in arabica. When the fading is more pronounced around the edges of the beans (which turn whitish) then this suggests the coffee was taken off the drying racks or grounds too early, or it was stored in moist, humid conditions, without adequate air circulation. If some of the beans are also generally softish and whitish then the experienced buyer knows such a coffee will never make it to the specialty market, let alone the roasted whole bean segment. Such a sample may find its way directly to the waste bin because such coffee has already lost its fresh taste and will definitely show a dull (bland) and common (ordinary) liquor.

    Prolonged storage can be another cause of loss of colour (and quality!). In this respect the Mesoamerican Development Institute (www.mesoamerican.org) carried out interesting experiments in 2005 in Costa Rica, storing green coffee in airtight cocoons and comparing quality against coffee from the same batch stored in the conventional manner. The two-piece hermetic storage cocoon consists of a top cover and bottom floor that are joined with a PVC tongue and groove zipper, similar to those used to close environmental safety suits. Coffee stored in this manner was found to have retained colour, flavour and quality much better, also over prolonged periods. Details of the research are available on www.mesoamerican.org.
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