Chilling Sensitivity

Many commodities native to tropical and subtropical growing regions did not evolve any tolerance for cold, because they never experienced it. For these commodities, temperatures well above freezing — temperatures that would be entirely safe for a temperate commodity such as an apple or a cabbage — are enough to cause lasting physiological damage. The mechanism is generally understood as membrane and metabolic dysfunction that sets in below a threshold specific to the commodity and cultivar, and the resulting injury is cumulative: a brief exposure at a marginal temperature may cause little harm, while the same temperature sustained for longer, or a lower temperature for a shorter time, can cause serious damage.

Chilling sensitivity is a property of the commodity and cultivar, not a quantity read directly off an instrument, which is why this entry has no associated measurement method. It is characterised experimentally: samples are exposed to controlled cold conditions for a set period, then rewarmed, and the injury that subsequently develops is scored against a defined scheme. That is an experiment about how a commodity or cultivar behaves under exposure, not a routine measurement performed on an individual lot, and the resulting classification is documented in commodity storage guidance rather than obtained from a store-floor reading.

• Pitting
• Water-soaking
• Internal browning
• Failure to ripen, or uneven ripening
• Increased susceptibility to decay

Several of these symptoms overlap with other storage disorders and are only confirmed as chilling injury by knowing the exposure history — see Internal Quality for how internal symptoms are assessed and why appearance alone rarely confirms a cause.

The opposite misreading of chilling sensitivity is just as costly as ignoring it: treating sensitivity as a reason to avoid cooling altogether. A chilling-sensitive commodity still respires, still generates heat, and still benefits from prompt cooling to manage decay and quality loss — see Precooling and Cold Chain. What differs for a sensitive commodity is not whether to cool it, but how far: it must be held above its chilling limit rather than at the lowest temperature that would otherwise be used for a non-sensitive commodity of similar type.

• Not freezing sensitivity — different mechanism, different temperature range, different symptoms.
• Not a fixed constant for a commodity — sensitivity varies with cultivar, maturity at harvest, growing conditions, and duration of exposure.
• Not a measure of injury already present — sensitivity is the susceptibility; the injury is a separate, later observation.
• Not a reason to withhold cooling — sensitive commodities still need cooling, just not below their limit.