The major health risk associated with coffee that has not been processed properly is the formation of ochratoxin A (OTA). OTA is a secondary metabolite of two toxigenic mould genuses, Aspergillus and Penicillium. It has been shown to be highly damaging to the liver and possibly carcinogenic (E. Petzinger and K. Ziegler, 2000). It is particularly troublesome as a contaminant because roasting temperatures don’t destroy it (Raters and Matissek, 2008); the European Union has imposed tight limits on OTA levels in roasted coffee beans, at 5–10 parts per billion, or 10–20 nanograms per gram (P. Poltronieri and F. Rossi, 2016), but they have imposed no such limits on green coffee. This means that in Europe, responsibility for ensuring that a safe product reaches consumers — as well as the legal liabilities associated with selling contaminated products — rests with coffee roasters.
Ochratoxin contamination may develop on ripe or unripe cherries. It can also develop on beans during and after processing, but the drying process presents the highest risk (P. Poltronieri and F. Rossi, 2016). OTA thrives in humid tropical conditions, and freshly harvested ripe coffee cherries represent ideal growth conditions for OTA–producing fungi, particularly during the first 3–5 days of drying (Schillinger et al., 2010). Wet-processed coffee appears to be less susceptible to infection by ochratoxin-producing moulds, probably because of the removal of the fruit pulp. This is because coffee pulp makes an ideal growing environment for OTA–producing fungi (M. Huch and C. M. A. P. Franz, 2014).