Cracking

A crack is a failure in tension. Tissue is pulled apart rather than crushed, and it parts along the line where it was weakest. This is a different failure from bruising, which is a compressive failure of cells beneath an intact surface, and it tends to affect different material: firm, turgid, low-elasticity tissue cracks where soft tissue would bruise. The same lot can do both — over-mature units bruising while immature ones crack under the same handling — which is one reason a defect record that lumps all mechanical damage together explains very little.

Surface or skin cracks

Fractures confined to the skin or cuticle. Common in tomato, grape, and cherry; the flesh beneath may be entirely sound and the unit still loses its barrier layer.

Growth cracks

Deeper fractures formed on the plant as tissue expands faster than the skin covering it can accommodate. Characteristic of carrot, tomato, and cabbage, and typically healed over and corky by the time of harvest.

Internal fissures

Fractures inside a kernel or a fleshy tissue with no external mark at all. The dominant form in cereal grains, and the reason grain cracking is discovered at milling rather than at intake.

Checking

Fine, shallow, often networked surface cracking. The term is used differently across commodities and processing contexts, which is part of the terminology problem this entry describes.

The classic pre-harvest cracking event is water. A crop that has been growing under dry conditions, whose skin has hardened and whose expansion has slowed, receives rain or irrigation; the tissue takes up water and swells faster than the skin can stretch, and the skin fails. Tomatoes crack radially or concentrically at the shoulder, cabbages split at the head, carrots crack longitudinally, grapes split at the berry, and cherries and plums crack at the surface. Nothing has been mishandled. The event is meteorological or agronomic, and it happened while the crop was on the plant.

• Rain or irrigation after a dry period, driving water uptake that outpaces skin expansion — the single most common cause of cracking in fruit and vegetables.
• Cultivar susceptibility, which varies substantially within every affected commodity and is a breeding target precisely because it is a field problem.
• Growth-rate changes during development, where a period of rapid expansion follows a check.
• Maturity at harvest, since over-mature fruit and over-mature heads crack more readily on the plant.
• Temperature swings and dew or surface wetness on fruit, affecting how much water is taken up through the skin.

One partial cue is age. A crack formed on the plant has usually had time to heal, so its edges tend to be dry, corky, and suberised, while a fresh crack is moist with exposed tissue that browns as it ages. The cue is useful and not decisive: a crack made shortly before harvest has not healed, a healed crack can be reopened by handling, and old and new cracks appear on the same unit. Time in store also blurs the distinction as fresh cracks dry out.

Cereal kernels crack for a mechanistically distinct reason: moisture gradients. A kernel that dries too quickly, or is dried with too much heat, loses water from its outer layers far faster than from its core. The outer material contracts around a still-moist interior, the resulting internal stress exceeds what the kernel structure can carry, and it fractures internally — while the outside of the kernel remains unmarked. The same thing happens in reverse when dried grain re-adsorbs moisture: the outer layers swell against a dry core, and the kernel fissures. Maize and rice are the classic cases, and in rice the consequence is measured commercially as broken grains after milling.

Stress cracking is the clearest example in this batch of a defect that is invisible when it is created and expensive when it is discovered. A fissured kernel looks like a sound kernel. It weighs the same, it flows the same, and it passes a visual intake inspection. It then breaks during hulling, milling, or handling, and the loss appears as breakage — a downgrade attributed to the mill, the sheller, or the handler, when it was caused by the dryer, possibly a season earlier. Fissures are detectable before that point by transmitted-light examination of a drawn sample, which is why that inspection exists.

Stress cracking should also be distinguished from the mechanical breakage that threshing, shelling, and augering inflict directly. Both end as broken kernels. But a kernel that arrives at the sheller already fissured breaks under handling that a sound kernel would survive, so a breakage problem attributed to equipment may in fact be a drying problem that the equipment merely exposed. Equipment adjustment will not fix that, and the investigation of a breakage complaint should include the drying history.

Cracking and splitting are not cleanly separable terms, and this entry does not pretend otherwise. The rough convention is that a crack is a partial fracture and a split is a fuller separation that opens the unit, but the usage is commodity-specific and inconsistent between standards, industries, and countries. Tomato growers speak of cracking for defects that cabbage growers would call splitting. Legume trade calls separated cotyledons splits; nobody calls them cracks. Grain trade calls internal fissures stress cracks and calls broken kernels breakage, and the boundary between a badly fissured kernel and a broken one is a matter of whether it happened to come apart yet.

The practical upshot is that the distinction is largely conventional rather than mechanistic — both are tensile failures, and the difference is one of degree and of what the local standard calls things. Which term applies to a given defect on a given commodity should be taken from the applicable grade standard, and data recorded under one term should not be compared with data recorded under another without checking that the definitions match. Two lots with different-looking defect records may have the same defect described in two vocabularies.

Because the causes divide into field and drying, so do the remedies, and neither is a handling measure. Post-harvest handling has a role only in not opening healed cracks and in not compounding fissured grain, and cracked units that arrive from the field can be removed but not repaired.

• For fruit and vegetables, treat cracking primarily as a field problem: cultivar choice, irrigation consistency, and harvest timing act on it, and no handling improvement will prevent cracks that formed on the plant.
• For grain, manage drying to the applicable sourced guidance for the commodity and dryer type, and control re-wetting of dried grain, since the reverse gradient fissures kernels just as drying does.
• Take drying history into account when investigating breakage complaints, rather than assuming the mill or the sheller created the damage it revealed.
• Sort out cracked units where the grade standard requires it, recognising that this removes the defect from the lot and does not address whatever caused it.
• Recognise that a crack, healed or fresh, is a defect in the barrier layer and therefore a route for wound pathogens; cracked fruit in store frequently ends as a rot record.
• Record the field history — rainfall or irrigation after dry weather, cultivar, maturity — so that a cracking finding can be attributed correctly rather than by default to whoever handled the crop last.