The Broken Cold Chain: How to Tell If Frozen Cargo Thawed and Refroze

Frozen cargo can look perfectly solid on arrival and still have failed. A reefer container that lost power for a day at a transshipment port, a load left on an unshaded apron, a warehouse that switched the room off overnight—the product partially thaws, then refreezes hard once cooling resumes, and by the time you open the box it is frozen again. The damage is done, it is often irreversible, and it is not always visible at a glance. This article is about reading the physical evidence so you can decide whether to accept, reject or test a frozen consignment.

What thaw-refreeze actually does to the product

When food freezes slowly—as it does on an uncontrolled refreeze—large ice crystals form and grow, and they puncture cell walls. On the next thaw, the liquid that was inside those cells runs out as “drip”. The result is loss of texture, loss of weight, loss of nutrients and a shorter remaining shelf life. For a whole fish it shows as a soft, mushy texture after cooking; for vegetables, a limp, watery product; for meat, excessive purge in the pack and a dry result. A single controlled freeze does little of this; a thaw and a slow refreeze does a lot.

Visual and physical signs on arrival

Before you accept the cargo, look for:

• Large ice crystals or a thick frost layer inside the primary pack — on a properly held product the frost is fine and light; heavy crystalline ice means moisture migrated during a warm spell and refroze
• A block of individually-quick-frozen product that has fused into a solid mass — IQF pieces that clump together have thawed enough to stick, then refrozen
• Cartons that are stained, sagging, or water-marked — drip escaped and refroze, or the carton got wet
• Pooled or channelled ice at the bottom of a carton or bag — liquid ran, collected and refroze in a shape gravity made
• A cavity or slumped shape where a moulded block has partly melted and reset
• Freezer burn — grey-white dry patches — which indicates long exposure to fluctuating temperature

None of these is proof on its own, but two or three together on multiple cartons across the load is a strong case that the chain broke.

The data trail

The reefer container’s own recorder logs supply air and sometimes return air temperature for the whole voyage. Pull that download—your forwarder or the line can provide it—and look for any period where the temperature rose above the setpoint and the frozen threshold. A power gap at a transshipment port often shows as a clean rise-and-recovery curve. If the shipper placed data loggers inside the cargo (and for high-value frozen goods they should), those give you the product temperature rather than the air temperature, which is what actually matters. Our guide to IoT temperature monitoring covers logger placement and reading the traces.

Also check for a simple freeze indicator on the pallet—a one-time device that changes colour permanently if the temperature crossed a set point. It will not tell you for how long, but it removes the argument about whether an excursion happened at all.

Confirming it: drip loss and a thaw test

If the visual signs are ambiguous, run a controlled check on a sample. Weigh a sealed pack frozen, thaw it slowly in a fridge, drain and weigh the product again. A high drip loss relative to what that product normally gives is objective evidence of ice-crystal damage from a thaw-refreeze cycle. For fish and meat you can also assess texture and odour after the controlled thaw. Do this on several packs from different pallets, keep the packaging, and photograph everything with the carton codes visible.

What to do with the finding

If you believe the chain broke, do not sign a clean delivery receipt. Note the condition on the delivery document, take dated photographs, retain the reefer download and any loggers, and pull representative samples. Then file promptly—time limits on cargo damage claims are short, and a claim supported by a temperature trace and drip-loss data is far stronger than one based on “it looked thawed”. Whether the liability sits with the carrier, the reefer plug operator at the transshipment port or the origin warehouse depends on where the trace shows the failure, which is exactly why the data trail matters.

Preventing it next time

Specify the setpoint and the acceptable range in writing on the booking. Require the shipper to place internal data loggers and a freeze indicator. Choose routings with fewer transshipments where possible—each plug-out and plug-in at a hub is a risk point, as we discuss in reefer container shipping. Ask whether the product was blast frozen properly at origin in the first place, because a product that was slow-frozen before it even shipped is already carrying crystal damage—see blast freezing versus sharp freezing. And insure the consignment for what it is worth.

Who is liable, and how the temperature trace assigns it

Liability for thaw-refreeze damage depends on where the chain broke, and the reefer download is usually what decides it. If the trace shows a clean temperature rise and recovery during a known window at a transshipment port—a period when the box was plugged out for transfer and not reconnected promptly—that points to the party responsible for reefer monitoring at that hub or to the carrier. If the trace is flat across the whole sea leg but the cargo still shows crystal damage, the problem was upstream: the product may have been slow-frozen at origin, or it warmed at the loading port before the container was powered. If the sea leg is clean and the damage appeared after discharge, look at the destination depot or your own transport.

This is why you never sign a clean delivery receipt for a suspect frozen load, and why you pull the reefer download immediately rather than weeks later. A claim backed by a temperature trace that pinpoints the excursion and by drip-loss data from a controlled thaw test is in a completely different position from one that rests on “the cartons looked wet”.

A receiving protocol for frozen consignments

• Before unloading, photograph the container seal, the reefer display showing supply and return temperature, and request the full voyage download
• During unloading, check product temperature with a probe on several cartons from different pallet positions, not just the door
• Inspect for fused IQF blocks, heavy internal frost, pooled or channelled ice, carton staining and slumped moulded blocks — across multiple cartons, not one
• Retrieve any internal data loggers the shipper placed and read them before distributing the stock
• If anything is doubtful, quarantine the load, note the condition on the delivery document, keep packaging and samples, and start the claim within the contractual time limit
• Run a controlled thaw and drip-loss test on sealed samples from different pallets and keep the results with photographs

We are not going to quote you an acceptable drip-loss percentage or a claim value, because both depend on the specific product, its normal baseline and your contract—a generic figure could weaken a genuine claim or inflate a weak one. Bring us the load and the data and we will help you read it. For frozen and chilled imports from China and the cold-chain freight to move them, contact DE International — see our cold-chain and freight services, our buying-agent service, and the catalogue.