Bleached, mottled, whitish, blotchy, soapy and discoloured beans
generally cannot be removed by size or density grading but there is no place for them in quality coffee (although there is probably some tolerance for them in the lower priced segment of the general market). Nearly all such beans are caused by moisture and drying problems, but discolouring can also be due to oxidization, contact with soil, metal, dirty water and so on. The gravity table can help but in the end the only effective way to remove these beans is through manual or electronic sorting.
Not only do such beans effectively ruin the coffee's green appearance but they also show up in the roast as softs or quakers, pales, mottled beans and so on, and they definitely affect the cup quality. The buyer of quality coffees will not tolerate such beans.
Modern sorting equipment
is capable of many and extremely varied tasks. The most recent developments use laser technology.
Such equipment can be quite costly though whereas in some countries sorting by hand is an important source of otherwise scarce employment.
Deciding whether to hand or machine sort depends on individual circumstances, the tonnages to be sorted, and the cost of labour. Smaller producers of specialty coffee usually give their coffee at least a quick going over by hand, especially if labour is relatively cheap. Some expend much time and care on sorting, depending on their target market.
Individual countries and operators have different ideas, systems and methods when it comes to sorting green coffee and there is no point in discussing these here because different circumstances pose their own particular requirements and problems. But there are two general principles which are important and which are always valid:
Know your sorting capabilities
. When preparing advance samples for dispatch abroad, ensure that your expectations of your sorting capacity do not exceed reality. It is only human to remove more rather than fewer defects from an advance sample 'as the coffee will be properly sorted in any case'. It is exceedingly annoying for the buyer to find later that the coffee is 'almost' but not quite as well sorted as the advance sample.
Without a good working environment and decent lighting people cannot sort coffee efficiently and correctly.
Many manual sorting processes still consist of people sitting on the floor in dark and dingy warehouses, each facing a heap of coffee. The sorters closest to the door can see the best - the remainder have to make do. This will never do for the preparation of quality coffee, whether arabica or robusta, because the sorting will be neither optimal nor even, and the entire operation is best kept hidden from visiting buyers altogether.
If sorting belts are too expensive, then at least invest in sorting tables and benches. These are easily made up by any competent carpenter. Such tables speed up the sorting process, which then is also more easily supervised. (Sorting belts are moving conveyor belts, usually with auto-feed and auto-advance, providing room for 12 or 24 sorters to sit on either side. Sorting tables are tables with a fluorescent light over them, seating 6 or 8 people. The tabletop is divided into squares with raised edges. A small hole in each square allows sorted coffee to fall into a bag hanging underneath; rejects go into receptacles fixed to the table's edge.)
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