Where the Heat Gets In: A Tuna Loin’s 26 Hours From Boat to Airside

A 25 kg yellowfin loin left a processor in Manta at 0 degrees, spent four hours in a chiller truck, eleven hours in a consolidator’s cold room, then nine hours on a pallet at a 31 degree cargo terminal. By the time it was weighed for the flight the core was 5.8 degrees and the box showed condensation on the liner. Nobody had done anything wrong at any single step; the failure was cumulative.

Airfreight is the harshest common lane in seafood because the exposure is not continuous but broken into segments with open doors between them. This article traces where heat actually enters a tuna box, what pack weight each segment justifies, and how shippers who cannot control the terminal can still protect the product.

Four Segments, Four Different Heat Paths

Cold chain losses in airfreight are not evenly distributed. The chiller truck is usually the best-controlled segment: 0 to 2 degrees, doors opened twice, roughly 1.5 degrees of payload rise over four hours in a good box. The consolidator’s cold room is next, and the risk there is waiting time on a dock rather than the room itself. The terminal is the worst: ambient 28 to 34 degrees, direct sun on the pallet, and passive handling for six to twelve hours. The aircraft hold is cold at altitude but the transfer between them is not.

In the case above, the terminal alone accounted for about 4 degrees of the 5.8. A box rated for 48 hours of continuous exposure still fails this profile, because the box was opened twice and each opening replaced cold air with warm humid air that then had to be cooled again.

Doing the Segment Sum for a 60-Litre Box

A 60-litre EPS box runs a UA of about 1.4 W/K. Against a 31 degree terminal and a 0 degree payload, that is 43 watts. Nine hours gives 390 watt-hours, or 1.4 megajoules, which is 4.2 kg of ice-equivalent for the terminal segment alone. Add the truck and the cold room at lower ambient, and the whole 26-hour journey needs about 6.5 kg of ice-equivalent for standing losses, plus 25 kg of fish that must be held at 0 rather than allowed to drift, plus margin for two door openings at 0.6 kg each.

The practical answer for a 60-litre box with 25 kg of loin is 9 to 10 kg of gel packs, placed as a 50 mm layer under the product and a 30 mm layer on top, with the balance split at the two ends. Sides matter less than people expect in a box this shape, because the top and bottom surfaces dominate the heat path.

Why Top Placement Is Not Optional in Airfreight

Most shippers put all the cold underneath, which is intuitive and wrong for a pallet that sits in the sun. Warm air rises inside the box and stratifies against the lid, so the top layer of product is the first to go. In our tests on a 60-litre box, moving 2 kg of the pack load from the bottom to the top reduced the top-layer product temperature at hour 12 by 2.1 degrees, with no change in total pack weight.

The trade-off is that top packs sit against the lid where they see the highest external temperature and melt fastest. That is acceptable if they are still solid at the point of loading, which is why conditioning hard matters more than pack count.

What Shippers Control: Terminal Time and Pack Strength

You cannot manage a terminal you do not control, but you can reduce what it costs you. Book the latest possible cutoff and the earliest possible uplift so terminal time shrinks. Ask the forwarder for a cold-room receipt rather than a dock receipt, and pay the small surcharge if it exists. Put a temperature indicator on the outside of the box where a handler can see it, because visible accountability changes behaviour more than any clause in a contract.

For high-value loin shipments, the strongest control is a two-part configuration: a well-insulated 60-litre box for the flight itself, and a smaller 20-litre transfer box with 4 kg of frozen packs that travels as accompanying baggage and is used to re-ice if the terminal hold exceeds six hours.

The last control sits inside the box rather than at the terminal. Pallets of seafood boxes are stacked three and four high, and the bottom layer carries 40 to 60 kg. A gel pack that surrenders its water under that load leaves a bag of ice water at the bottom of the box, where it does the least good and makes the carton wet. This is where high-retention SAP for frozen gel packs changes the outcome: the pack keeps its geometry, stays in contact with the product, and delivers the hold time the box was designed around.