Mould Incidence

Mould incidence is assessed by drawing a representative sample from the lot and examining it, usually visually, for kernels or units showing infection or surface fungal growth. The result is reported as a proportion — by count, by mass, or as colony-forming units per gram where a microbiological plate count is used instead of a purely visual assessment. Because it is fast and does not require a laboratory, it is used widely as a first-line screening signal at intake and during storage inspection.

As a screening signal, mould incidence is useful for flagging lots for closer attention, for tracking trends in a store over time, and for triggering aeration or turning decisions. It is not, by itself, a determination of whether the lot meets any food- or feed-safety requirement.

The relationship between visible mould and mycotoxin contamination is asymmetric and counterintuitive. On one side, a lot can show substantial visible mould growth from species that never produce toxin, or from a toxigenic species under conditions that did not favour toxin formation — visible mould, on its own, does not establish contamination. On the other, far more consequential side, a lot with no visible mould at all can already carry mycotoxin: the toxin can have been produced earlier by a fungus that has since died, can be distributed unevenly through the lot away from any visibly affected kernel, and survives cleaning, sorting, and in many cases processing.

Temperature probes are used alongside visual inspection to monitor stored lots because active fungal and insect metabolism generates heat, and a rising temperature near a sensor can flag a developing hot spot before it becomes visible at the surface. This makes temperature monitoring a useful, low-cost, continuous surveillance tool.

It is, however, only a proxy, and a limited one. A stable reading at the sensor is not evidence that the lot is free of mould or insects — activity elsewhere in the bulk may not yet have reached the probe, or the sensor spacing may be too coarse to detect a localised pocket. Cooling a lot that has already self-heated slows further biological activity, but it does not remove any mycotoxin that has already formed; a temperature record is a monitoring tool for storage conditions, not a safety clearance.

Mycotoxin contamination in a bulk lot is characteristically heterogeneous: a small number of badly contaminated kernels, clustered rather than evenly spread through an otherwise clean lot, can be responsible for the entire result. This makes sampling, not analytical precision, the dominant source of error in any toxin determination — a poorly drawn sample can produce a result that misrepresents the lot in either direction, regardless of how accurate the laboratory method used on that sample is.

Establishing whether a lot exceeds an applicable mycotoxin limit therefore requires both a properly designed sampling protocol and a validated laboratory method, applied together. This entry does not state any toxin limit; the applicable food or feed safety regulation sets maximum levels for the specific commodity, toxin, and jurisdiction.