Wrapping respiring produce for export without spoilage

Harvest does not switch the product off. Fruit and vegetables go on respiring inside the case — taking in oxygen, giving off carbon dioxide, water vapour and heat — for as long as they are alive. A wrapped pallet of produce is therefore a small continuous heat source and a small continuous humidifier, running from the packhouse until somebody opens the box.

The warmer it gets the faster it respires, and the faster it respires the warmer it gets. Slowing that loop down is what the entire cold chain exists for. Every layer you put around the product either helps the cooling reach it or stands in the way, and the pallet wrap is the last layer you add and the one sitting closest to the cases.

A solid stretch film is an airtight skin. It stops respiration heat leaving, so the middle of the stack stays warm long after the outside has cooled. It stops water vapour leaving, so humidity inside the wrap climbs until the inner face of the film is below the dew point of the air trapped against it. Free water forms there and runs back down onto the load.

From that point the damage is ordinary and expensive. Wet corrugated loses its stiffness, so the columns that were carrying the stack stop carrying it and the pallet leans. Labels lift and print runs. Mould starts anywhere warm and damp and does not need long. And the ethylene the fruit gives off has nowhere to go, so it sits in the wrap with the fruit producing it.

Almost none of it happens in the first hour. Pre-cooling that never reached the core of the pallet catches up with you three days into a sea crossing, when the ripening is a week ahead of the paperwork. A load wrapped warm and pushed straight into a chilled container sweats again at every temperature change on the route: dock, ship, quay, transhipment, delivery yard.

By the time it is opened at the far end, the pallet is judged on how it looks. Damp cartons, a leaning stack, mould in one corner, spoiled labels. Those are the grounds a receiver refuses on, and every one of them is downstream of heat and water that were sealed in at the moment of wrapping, thousands of kilometres earlier.

Aerosonic is a macro-perforated stretch film built for exactly this load. Hole size and perforation count are engineered to the product rather than taken from a standard pattern, so respiration heat and vapour leave the pallet instead of collecting behind a plastic skin, and cold air from the store or the container can reach the cases in the middle of the stack. It puts roughly half the metres onto the pallet that solid 23-micron film does.

Breathability does not cost you containment. In Toreto's own wrap tests in August 2026 — same pallet, same machine, same power stretch and tension settings — 16-micron Aerosonic held 10 kg per square inch on 66 g of film per pallet, against 9.9 kg per square inch on 200 g for 23-micron solid film. Cost per pallet varies with film price and pallet size.

Not every perforated film behaves that way. In our own team's field experience, most of it is punched flat on the roll and then barely opens, because the base material will not stretch as the film is applied. The buyer pays for perforation and receives a fraction of the airflow. What matters is the aperture on the finished pallet, not the pattern on the roll.

Aerosonic Lite is the version for produce that is respiring hard and cannot wait for the cold to work its way in. It is pre-stretched over 300% and macro-perforated with large aeration holes carried by reinforcing bands, so it wraps in a single layer where competing breathable materials need several. Hole size is set to the load rather than fixed.

Trying a breathable film costs less than most exporters expect. Supersonic and Aerosonic are made from the same materials and perform the same, so a line can move between solid and breathable at the same cost per pallet with the machine settings unchanged. Other breathable films on the market typically cost up to 100% more in use and want settings of their own.

Perforation gives air a route through the film. It does not give air a route through the load. Solid-walled cases butted tight together, with no vent holes and no channel up the middle of the pallet, will ventilate their outer face and nothing else. Vented crates, vent holes that line up between layers and a deliberate air channel in the pallet pattern are what turn perforation into cooling.

Then do not undo it at the end of the line. A solid hood, a shrink cover or a second wrap of solid film over a breathable one puts the vapour barrier straight back, and the load is sealed again with all the airflow you paid for trapped underneath.

Apply the inside face of the film to the goods; it adheres better. Two revolutions at the base to lock the load to the pallet, then spiral up with a 20–30 mm overlap and two revolutions at the top. Tension enough to secure the load fully, but not so much that you crush it — a crushed case is a wet case waiting to happen.

On tall, heavy or unstable produce pallets, spiral back down to the base. The criss-cross adds stability on slippery loads, which is most of what a container does to a stack over a long crossing. Finish with a clean cut or tear; there is enough tack to swipe the tail down by hand.