Superficial Scald

Superficial scald is superficial in the literal sense. The browning occupies the skin and the cell layers immediately below it, and cutting through a scalded patch normally reveals flesh of ordinary colour and texture. That geometry is diagnostically useful in principle: an internal disorder gives sound skin over discoloured flesh, and scald gives discoloured skin over sound flesh, so the cut fruit distinguishes them where the intact fruit cannot. It is worth stating plainly that this is a principle rather than a rule that always holds — severe or advanced scald can involve tissue below the surface, and a fruit may carry scald and an unrelated internal disorder at the same time, in which case the cut surface shows both and attributes neither.

The disorder is associated with the oxidation of compounds that accumulate in the skin during storage, and the browning that results is the visible endpoint of that chemistry. What matters for anyone handling fruit is that this is a process occurring in the skin over time in store, driven by the condition of the fruit when it went in and by the environment it has been held in since — not an injury inflicted at a moment that could be located in a handling record.

Latency is the operational heart of this disorder. At the moment a lot is graded and placed into store, fruit that will scald badly and fruit that will not are indistinguishable — there is no early symptom, no partial expression, nothing for an inspector to grade against. The disorder develops through the storage period and frequently declares itself only when fruit is warmed for market. The decision to commit a lot to long storage is therefore always made without information about the defect that may end it, and the loss is discovered at the point where the most storage cost has already been incurred.

• Storage-in inspection cannot detect scald: no symptom exists yet to detect.
• Grading standards applied at intake describe the fruit as it is, not the disorder it will develop.
• Because expression often follows warming, a lot can pass inspection leaving the store and fail after it arrives.
• Risk assessment before storage rests on cultivar, growing conditions, and maturity rather than on inspecting the fruit for the disorder.
• By the time scald appears, the storage period that produced it is over and cannot be corrected.

Scald is regularly explained as chilling injury, and the explanation is wrong. It is a plausible error: the disorder appears after long cold storage, it involves browning, and it often becomes obvious on warming — a description that reads like chilling injury written out. But apples and pears are not chilling-sensitive in the sense that banana, avocado, mango, and cucumber are. They do not carry a high chilling threshold that a cold store violates; they are routinely and correctly held close to their freezing point for months, and that practice is not the cause of scald. Calling scald chilling injury implies the store was too cold and points management toward raising temperature, which is the wrong lever.

The confusion with controlled-atmosphere injury runs differently and is harder to dismiss. Controlled-atmosphere storage is used on pome fruit partly because it suppresses scald, so it is a genuine control. An atmosphere that is wrong for the cultivar, though — carbon dioxide too high or oxygen too low — causes injury of its own, and some of that injury browns the fruit. The same store can therefore be the reason a lot did not scald or the reason it is brown for a different cause entirely, and appearance will not say which. That question is answered by the atmosphere record and by knowing what the cultivar tolerates, both of which come from sourced guidance and qualified operators rather than from the fruit.

Nothing recovers scalded fruit — the skin does not repair, and a lot found scalded at the end of storage is a loss already incurred. Every useful measure acts either before the fruit is stored or through the conditions maintained during storage, and the largest single factor is the choice of what to store in the first place.

• Treat cultivar as the primary risk variable: susceptibility differs greatly, and a prone cultivar committed to long storage carries a risk that no storage practice removes entirely.
• Take account of maturity at harvest and growing conditions, which modify susceptibility and are fixed before the fruit reaches the store.
• Specify storage conditions and, where used, controlled atmospheres against sourced guidance for the cultivar, recognising the technique controls scald when right and injures fruit when wrong.
• Manage ethylene and the ripening environment as part of the storage regime, since the storage physiology that produces scald is bound up with the fruit ripening state.
• Match intended storage duration to the lot: latency means the disorder is a function of time in store, and a susceptible lot marketed early may never express it.
• Where browning appears, use the atmosphere and temperature record to separate scald from atmosphere injury rather than reading it from the skin.