Freezing Injury

Harvested tissue is mostly water, but that water is not pure — it carries sugars, acids, salts, and other solutes that depress the temperature at which it crystallises below the freezing point of pure water. This is why no single freezing temperature can be quoted for fresh produce, and why this entry quotes none. The depression depends on the concentration of dissolved material in the tissue, which varies by commodity, by cultivar, by maturity, and even between parts of the same unit. A figure taken from one commodity does not transfer to another, and a figure that appears authoritative but is applied to the wrong commodity is worse than no figure at all.

Once crystallisation does begin, the damage is structural. Ice forming in the spaces between cells draws water out of the cells themselves, dehydrating and distorting them; ice forming inside cells punctures membranes directly. Either way the compartments that keep the tissue organised are breached. While the lot remains frozen this may be entirely invisible — the tissue is held rigid by the ice that is destroying it. On thawing, the contents of the ruptured cells escape into the intercellular spaces, air is displaced by liquid, and the tissue takes on the characteristic translucent, glassy, water-soaked appearance and leaks freely when cut or handled.

Both disorders can leave water-soaked tissue, which is precisely why the shared cue is useless for separating them. What distinguishes them is not the endpoint but the history that produced it, and history is not visible in the tissue.

In practice the separation is made from recorded temperature history rather than from the lot, and where no adequate record exists the question may simply not be answerable. A useful asymmetry is that freezing injury commonly appears as a localised pattern — the units nearest a cold-air discharge, against an exterior wall, or on the face of a pallet exposed to an open door — because freezing is usually a local excursion rather than a whole-store condition. Chilling injury is more often distributed across the lot, because the whole store was set wrong. This is a hint about where to look, not a diagnosis; a store with an even freezing excursion, or a lot with a cold spot below the chilling tolerance, will break the pattern.

• Control failure in a cold store or vehicle: a faulty sensor, a failed controller, or a set point placed too close to the commodity freezing point with no margin for variation.
• Cold spots within a store that is correctly set on average — directly in the evaporator discharge stream, against uninsulated surfaces, or where air short-circuits through a poorly stacked pallet.
• Refrigerated transport in which produce sits in the delivery air stream rather than being loaded to allow air to pass around it.
• Ambient freezing exposure at points where the chain is not controlled at all: on a loading dock in winter, in an unheated staging area, or during an open-air transfer.
• Delayed field heat removal followed by aggressive over-correction, where a store is driven hard to recover temperature and overshoots.
• Produce held very close to its freezing point deliberately, to extend life, where the margin for error is inherently narrow and normal variation can cross it.

The recurring theme is margin. Holding close to the freezing point is a legitimate practice for some commodities and is why several are stored at very low temperatures without harm — but it removes the buffer that absorbs sensor drift, stratification, and door openings. Where that margin should sit for a given commodity is not a universal number and is not stated here; it comes from sourced post-harvest guidance for the commodity, and where guidance is silent the safe course is a conservative one.

There is no treatment. Frozen tissue does not recover, and a thawed lot cannot be restored by any handling, packaging, or storage measure — the only useful interventions occur before the ice forms. Management is therefore entirely about control, margin, and monitoring of the environment the produce is held in.

• Set holding temperature against sourced guidance for the specific commodity, with a deliberate margin above its freezing point rather than at it.
• Map cold stores and vehicles for local variation rather than trusting a single control sensor; the coldest point in the space is the one that determines whether a lot freezes.
• Stack and load so that delivery air passes around produce rather than through it, and keep units out of the direct discharge stream.
• Protect the uncontrolled links — docks, staging areas, and transfers — where ambient exposure, not equipment failure, is the usual cause in cold climates.
• Record temperature continuously through the chain, since a brief local excursion that causes irreversible damage may be over long before anyone looks.
• Where water-soaked tissue is found, treat the temperature record as the evidence and the appearance as the prompt, since freezing and chilling injury cannot be separated by looking.