Thaw-in-Transit: Pads for Product That Defrosts Between Two Docks

A load of 26 pallets left a plant in northern France at -18 °C, sat at a hub for four hours in July air, and reached Manchester 31 hours later at -9 °C. Twenty-two pallets were fine. Four had partial thaw on the outer face of the bottom layer and left 40 to 60 millilitres in each carton. Two days later the customer filed a claim for staining across 180 cases; the pallet base liners had done nothing because there were none.

Thaw does not only happen in a thaw room. Any journey with a consolidation stop, a door opening at a hub, or a reefer set to the wrong setpoint produces partial thaw in transit, and the liquid has nowhere to go. This article covers where transit thaw occurs and what absorbent placement can do about it.

Where the Water Comes From on a Moving Load

Three mechanisms produce liquid in a trailer. The first is genuine temperature rise above the product freezing point at the outer faces, usually because the reefer is set to -18 but the load was only at -14 when it left, and the unit cannot pull down fast enough during the first six hours. The second is condensation: warm humid air entering during a door opening condenses on cold cartons and runs down. The third is ice crystal damage, where product that has been through several partial freeze-thaw cycles releases purge at the slightest temperature rise.

Only the first produces real drip, but from the customer side all three produce the same stained carton and the same claim.

Why Pallet Liners Beat Carton Pads in Transit

A carton pad intercepts liquid, but it intercepts it at the wrong scale. Thirty cases per layer at 20 kg each produce 12 to 20 litres of potential drip across a pallet, which no carton pad can hold and no pallet needs to. What a pallet needs is a base liner with a 1 to 2 litre capacity that catches what runs down the stack, combined with a carton pad that stops liquid reaching the carton wall where it shows.

The practical arrangement is a 900 by 1,300 mm absorbent base sheet at 300 to 400 gsm under the bottom layer, plus a 200 gsm pad in each carton for product contact. The base sheet handles the aggregate, the carton pad handles appearance.

Reefer Settings, Pre-Cooling and the Four-Hour Hub

Most transit thaw is preventable at the dock. Load product at or below -18 °C, not at -12 with a note that the reefer will finish the job. Preheat the trailer. And avoid hubs with ambient cross-docking for frozen loads, or insist on a frozen bay.

Where a hub stop is unavoidable, the four-hour exposure matters more than the temperature. A pallet at -18 °C sitting in a 25 °C dock for four hours gains about 2 to 4 °C at the outer cartons and produces condensation but no drip. The same pallet left for twelve hours will have a thawed outer layer.

Writing Absorbency Into the Delivery Specification

If a customer requires no visible staining on receipt, that requirement has to travel back into packaging. State the absorbent placement in the logistics agreement: base liner grade and size, carton pad grammage, maximum hub dwell time, and the reefer setpoint with a pre-cool requirement.

Then measure it. A temperature logger per pallet for the first ten shipments tells you whether the specification is achievable before you commit to a claim exposure.

Transit absorbency is a different job from thaw room absorbency, because the load is distributed and the liquid arrives late. Our SAP base liner and carton pad stock for cold-chain transit covers both scales.