Chilling Injury

Chilling injury and freezing injury are frequently spoken of together and are not the same event. Freezing injury is a physical process: water in the tissue crystallises, ice ruptures cell structure, and on thawing the tissue collapses into a translucent, water-soaked, leaking state. Chilling injury involves no ice at all. It is a progressive physiological disturbance — membrane function, respiration, and ripening metabolism are disrupted — occurring at temperatures well above freezing in commodities that cannot tolerate them.

The distinction matters operationally because the two have different remedies. Freezing injury is prevented by keeping the produce above its freezing point; chilling injury is prevented by keeping chilling-sensitive produce above a much higher threshold that varies by commodity. A cold room running correctly for apples can be actively injuring bananas in the same building. Chilling sensitivity is a property of the commodity, not a fault of the equipment, and the temperature that is good practice for one commodity is a defect-generating condition for another.

Surface pitting

Sunken depressions in the skin where groups of cells have collapsed; common in cucumber, sweet pepper, and citrus.

Failure to ripen normally

Chilled fruit may soften unevenly, fail to develop colour or aroma, or ripen to a poor eating quality; banana, mango, avocado, and tomato are characteristic.

Internal discolouration

Browning or greying of flesh or vascular tissue that is invisible from outside and found only on cutting.

Water-soaked lesions

Translucent, sodden areas of tissue — a presentation shared with freezing injury and with several rots, which is why it is not diagnostic on its own.

Secondary decay

Chilling-weakened tissue is readily colonised by pathogens, so the visible endpoint is often a rot rather than the underlying disorder that permitted it.

Because the endpoint is so often decay, chilling injury is systematically under-recorded: the lot is written off as a rot problem and the temperature history that predisposed it is never examined. Where a commodity shows disproportionate decay after a normal-looking cold chain, the holding temperature relative to the commodity's own tolerance is worth reviewing.

• Holding a chilling-sensitive commodity at a temperature below its tolerance — most often because a store, vehicle, or display is set for a generic "cold" target rather than the commodity's own.
• Mixed loads in which commodities with incompatible temperature requirements share a single controlled space.
• Cumulative exposure across several links of the chain, where no single leg is clearly at fault but the total dose is injurious.
• Cold spots within an otherwise correctly set store — near evaporator discharge, against walls, or in poorly stacked pallets.
• Pre-existing field or maturity condition: immature fruit is generally more sensitive than mature fruit of the same commodity.

The applicable lowest safe temperature for any given commodity — and, for some, the cultivar and maturity stage that modify it — is not a universal figure and is not given here. It is set by sourced post-harvest guidance for that commodity; consult FAO, USDA-ARS, or the relevant extension handling references before setting a store.

There is no treatment for chilling injury once it has occurred; the damage is not reversible and the affected lot cannot be recovered. Management is entirely preventive and consists of holding each commodity within its own tolerated range through every link of the chain, which requires knowing that range per commodity rather than per cold room.

• Set holding temperature by commodity against sourced guidance, not by what the room is capable of reaching.
• Segregate chilling-sensitive commodities from those that tolerate near-freezing holding rather than compromising on a single intermediate setting.
• Monitor and record temperature through the whole chain, including transport and display, so that a delayed symptom can be traced to the leg that caused it.
• Treat unexplained decay or ripening failure after cold holding as a prompt to review temperature history, not only sanitation.