Heat Damage

Dryer heat

Artificial drying that uses air hotter than the grain and its end use can tolerate scorches the outer layers or, in more severe cases, the whole kernel. Seed and malting grain are dried at lower temperatures than grain destined for feed precisely because germination and enzyme activity are more heat-sensitive than the kernel’s appearance.

Self-heating in store

Damp grain respires, generating heat and moisture; mould and insect activity in the same bulk add further metabolic heat. In a poorly aerated or poorly monitored store, this heat accumulates faster than it dissipates, and the surrounding kernels darken from prolonged exposure to elevated temperature from within the bulk rather than from an external heat source.

Because both routes can produce visually similar darkened or scorched kernels, heat damage recorded in a lot does not by itself indicate which route produced it, and the two imply different things: dryer heat points to an equipment or process issue at drying, while self-heating points to a storage-management issue that may still be active and worsening.

Heat damage is one of the defect categories explicitly defined and scored within the grade standards used for major cereals and oilseeds, including the standards issued for wheat, corn, and soybeans. Its presence, above whatever level the applicable standard treats as a grading threshold, can move a lot to a lower grade regardless of how the lot performs on other measured attributes.

Because heat damage is graded as a defined category rather than assessed informally, its scoring is tied to the specific edition of the standard in force, and buyers and sellers should confirm which edition and which grade factor definitions apply to a given contract.

Distinguishing heat-damaged kernels from other forms of discoloration — weathering, natural pigmentation, or damage from other causes — is not left to unaided visual judgement. Grading authorities issue reference or interpretive line samples that define the boundary between heat-damaged and non-heat-damaged kernels, and graders compare submitted kernels against these physical or photographic references rather than relying on personal judgement alone.