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A moisture content value ostensibly supporting no growth may contain a few beans wet enough to support slow growth and if stored in the coffee chain for long enough could spoil. In addition, respiring organisms, including insects, produce water from carbohydrate that could slowly accelerate local deterioration. Lastly, high inoculum levels are known to overcome conditions normally stringent enough to prevent microbial growth, a poorly understood phenomenon sometimes referred to as the 'inoculum effect'.The maximum moisture content for exportable coffee as recommended by the ICO (ICO Resolution 420 [.pdf]) is 12.5%. If this level of moisture is maintained throughout the market chain using proper sampling techniques and moisture measurement devices, there should not be a significant risk of OTA contamination in coffee.
