• Moisture content and drying

    There is no exact standard for ideal moisture content. Not all coffee is the same, and circumstances differ from country to country. In general, 11% is probably a good target for most coffee. In any case roasters are increasingly insisting on a maximum moisture content on arrival. Coffee above 12.5% moisture should never be shipped.

    If past experience suggests buyers are generally satisfied then stick to good established practice and monitor the moisture content regularly. Remember that when coffee is dried on flat surfaces (such as tarpaulins or concrete) it will heat up and thus dry out more rapidly than when it is spread on raised tables or trays that allow air to circulate around it. When getting close to the moisture target, monitor every hour. Always use properly calibrated moisture meters and test them regularly, before each season. If in doubt about the exact percentage, take the coffee off a little earlier rather than letting it become noticeably over-dried. This is especially recommended if decent storage sheds or, better still, ventilated bins or silos are available for conditioning.

    Apart from later loss of cup quality, under-drying may also cause mould. In severe cases, under-dried coffees may develop fungi and moulds. These have always been undesirable but increasing consumer attention to mycotoxins in agricultural produce, specifically ochratoxin A (OTA), is a real cause for concern for some coffee producers. Clean, proper and efficient drying and storage of coffee is probably the best defense against mould growth and its potential consequences. This and other food safety issues are reviewed in detail in Chapter 12 - Quality control issues.

    To repeat once more: many receivers stipulate a maximum acceptable moisture content on both shipment and arrival. Producers and exporters need to develop appropriate moisture content management techniques if they are to cope with this.

    Over-drying costs money. This makes it as serious as under-drying: not only is weight, and therefore money, lost unnecessarily, but the accompanying loss of colour also translates directly into lower liquor quality. When moisture drops below 10%, aroma, acidity and freshness begin to fade away and at 8% or below they have completely disappeared. For this reason the ICO wants to see shipments of coffee below 8% moisture content prohibited.

    Like under-dried coffee, over-dried coffee should not be mixed with correctly dried coffee. They are not compatible. Remember also that climatic conditions in many storage sheds are not ideal: they may be keeping the coffee dry but they are certainly not keeping it cool and the coffee may therefore continue drying out. Quality loss due to over-drying cannot be reversed, and is unacceptable. Over-dried coffee also breaks up more easily during milling. This increases the percentage of ears, shells and broken beans, which further reduces both the quality and the value.

    Finally, do everything possible to avoid letting coffee sit around endlessly after it has been containerized for export. This can be especially problematic for landlocked countries from where coffee must travel long distances to the port of shipment. If containers are kept in the open, exposed to open sun in holding grounds, on railway flatcars or trucks, then this can lead to overheating and condensation. See 05.02 Shipping in containers.

    Over-drying also affects the way a coffee roasts. Coffees with a moisture content as low as 8% may certainly take the average specialty roaster by surprise. This is because such coffees tend to roast to completion much faster than these roasters expect. Smaller specialty roasters do not always have moisture meters, and they can and do get into trouble with such coffees. Quite apart from the reduction in acidity and flavour that over-drying causes, the end-user may also be embarrassed - all good reasons never to buy that coffee again.
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