• OTA - in coffee


    In coffee OTA is produced by fungi of the Aspergillus genus (A. ochraceus, A. carbonarius, A. niger). It is mostly concentrated in the husk, which suggests that naturals (coffees dried in the cherry) are most at risk of contamination. Identified factors affecting mycotoxin levels in the coffee chain include:

    • Environmental factors: temperature, moisture, mechanical injury (insect or bird damage, micro-organisms);
    • Harvesting factors: crop maturity, temperature, moisture;
    • Primary processing, drying, removal of defects;
    • Storage: temperature, moisture;
    • Distribution and processing: condensation;


    Studies have shown that inadequate sun drying of cherries leads to OTA formation in the pods and parchment husks, and that defectives (including black beans), pods and husks (and dust) are the most important sources of OTA contamination in green coffee. The drying stage is the most favourable time for the development of OTA. Adequate drying to uniformly low moisture levels and avoiding local wet spots, caused for example by uneven drying, rewetting or condensation, is crucial in prevention. Simple and cheap devices for solar drying of coffee can be of great help in improving drying practices, including prevention of rewetting by rain or dew.

    Tests have also shown that the presence of an earthy/mouldy smell in green coffee is an early indicator of the presence of mould damage - of course not every mould is OTA-forming, but an earthy smell (or cup) should trigger further investigation. Similarly, visually clean coffees that show no visible damage (rewetted bags/beans, broken beans, insect-damaged beans) are very much less likely to be significantly contaminated. The use of green coffee with a higher contamination level than 15 ppb is not recommended. Given a reduction of OTA contamination through processing of 2/3rd (this is a conservative figure, used to be on the safe side as the actual reduction may be higher), green coffee with a contamination level of less than 15 ppb can reasonably be expected not to present any problem in the finished coffee.

    The preventative steps listed in sections 12.08.03 and 12.08.04 apply as much to wet processed coffees as they do to dry processed (natural) arabica and robusta. Good housekeeping is essential.

    Prevention is currently the only available effective way at farm level to combat OTA although it should be noted that the removal of mouldy cherry, or the reprocessing of mouldy coffee, does not guarantee that the clean bean will be free from micro particles or spores.

    Visit www.coffee-ota.org for an overview of research work done and in progress.Visit also www.ecf-coffee.org and look under Publications for extensive, practical information on OTA as an issue in the production and trading of green coffee.

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