Hot-fill, canning and bottling: beating condensation on the line

A food or drink line does not hand you cold pallets. Hot-fill product goes into the container hot on purpose, so the heat is part of the process rather than an accident. Cans and bottles come off a tunnel pasteuriser carrying heat. Retorted product cools from the outside in. Even a cold-fill line palletises trays that have just been through a shrink tunnel.

Then the pallet behaves like a poor heat exchanger. The outer cases lose their heat in the yard within the hour; the middle of the load holds it far longer, hours after the outside feels cold to the hand. Whatever that trapped heat does next, it does inside the wrap, which is why the wrap is the first part of the process worth looking at.

Steel and tinplate first. Water collects in the rim of a can and under a shrink-wrapped tray, and rust blooms there. A rusted can is refused by the retailer even when the seam is perfect and the product inside is sound.

Then the labels. Water gets between the label and the container: wet-glue labels lift and slide, self-adhesive labels wrinkle at the edge, print smears and barcodes stop scanning. Then the board. A tray or case that takes up water loses compression strength, the stack settles unevenly, and the pallet arrives leaning. After a few days in a closed trailer, mould appears on the outer case.

None of that shows up on a report as a damaged carton. It shows up as a rejected load: a refused delivery, a return journey, a credit note, a re-pack, and a mark against you on the customer's supplier scorecard. The real cost is not the film; it is stock stopped at the customer's gate.

Solid film is an unbroken plastic skin, and it does two unhelpful things at once. It blocks water vapour, so the moisture the load is carrying has nowhere to go but the inside face of the film. And it blocks air movement, so the pallet holds its heat far longer and spends longer in the band where condensation keeps forming.

The mechanism is simple. Air holds moisture in proportion to its temperature; cool it below its dew point and that moisture becomes liquid on the nearest cold surface. Wrap a warm pallet, move it into a chill store or a night trailer, and the film cools first. Its inner face is now the coldest surface in the package, so the water forms there, runs down and drips back onto the cases.

The fix is not a drier plant or a colder store. It is to stop sealing the vapour in. A precision-perforated film lets warm air and water vapour leave the load as it cools, while still containing it and still keeping dust and pests out. The openings are engineered, not tears or slits.

Aerosonic is Toreto's breathable film. The hole size and the perforation count are set against the load rather than to a standard pattern: a pallet of hot-filled glass and a pallet of warm cans do not need the same open area, and neither does a load going straight into a blast chiller.

One warning, from Toreto's own field experience rather than a laboratory. Most rival perforated films will not stretch, so their holes never open up as the film is applied. The roll looks identical, the buyer pays for perforation, and the load gets a fraction of the airflow. Ask to see any breathable film run on your own pallet before you commit to it.

This is the objection every production manager raises, and it deserves numbers rather than reassurance. Toreto's own wrap tests, August 2026, ran the same pallet on the same machine at the same power stretch and tension settings, with the film weighed and the holding measured. Aerosonic and Supersonic at 16µ held 10 kg per square inch on 66 g of film, at roughly €0.32 a pallet. A 23µ solid film held 9.9 kg per square inch and needed 200 g, at roughly €0.48.

Those are Toreto's own measurements rather than estimates, and the cost per pallet moves with your film price and your pallet size. The reason the holes cost nothing in containment is that the containment comes from reinforcement inside the film, not from an unbroken skin. The reinforced films also ran about half the revolutions, so the same wrapper puts out twice as many pallets in a shift, which matters when the wrapper is the bottleneck at the end of a run.

A drinks plant rarely wraps one kind of pallet. Warm hot-fill product, ambient stock, empty containers and dry goods can all cross the same wrapper in a shift, and nobody wants to re-programme a machine between them. Aerosonic and Supersonic are made from the same materials and perform the same, so a line can switch between breathable and solid at the same cost per pallet on unchanged settings.

That is the practical difference between a trial that survives and one that does not. Other breathable films on the market typically cost up to 100% more in use and need their own machine settings, which is why they get tried once on a Friday and quietly dropped on the Monday.

Apply the inside face of the film to the goods, because it adheres better. Two revolutions at the base to lock the load to the pallet, spiral up with a 20–30 mm overlap, two revolutions at the top. For a heavy or unstable load, spiral back down to the pallet as well; the criss-cross adds real stability on slippery packs. Finish with a clean cut or tear.

Tension is where warm loads are different. Use enough to secure the load fully and not so much that you crush it: warm board is softer than cold board, and a setting that is right for a cold pallet can pull a warm one out of shape. Check the top and bottom courses on the first pallets of a hot run before you trust the whole batch to them.