Stop frozen blocks fusing: wrapping for blast-freeze

A pallet goes into the blast cell as a stack of separate cartons and comes out as a single lump. Someone has to break it apart before anything can be picked. Board tears, labels come away, corners crush, and a mixed pallet cannot be split across three orders.

Nothing about the product caused it. The cause is water, and it was already inside the wrap. Sealing a load in solid film traps the air that was around it at the moment of wrapping — the humidity of the packing hall, the product’s own moisture, the ice glaze on frozen goods. As the load cools, that vapour has nowhere to go, so it condenses on the coldest surfaces it can reach and freezes.

Those surfaces are the inner face of the film and the outer faces of the cartons. Water gathers in the narrow gaps where cartons touch, freezes, and bridges one carton to the next. It takes very little water, and the bill arrives as labour, damaged packaging and re-work.

A blast freezer works by driving very cold air across the product at speed. Wrap the pallet in a continuous plastic skin and that air stops at the outside. It goes around the load rather than through it, so the only route to the middle is conduction, carton by carton, from the outside in.

The load then freezes from its outer face inwards. The outside is at temperature while the core is still warm, so the pallet has to sit longer for the centre to catch up. That is more cell time for the same batch, and more time in the band where vapour is still moving inside the wrap looking for a cold surface to freeze onto. Slow freezing and fused blocks are one problem seen at two moments.

Aerosonic is a breathable stretch film with engineered perforations. Cold air passes through the wrap and through the load instead of stopping at the skin, so it reaches the middle of the pallet rather than working inwards from the edges. Blast-chilling and freezing run faster because the cold air gets to the product instead of queuing outside it.

The same openings carry the vapour out. Moist air leaves with the airflow instead of collecting on cold surfaces inside a sealed package, so there is no water sitting in the joints between cartons when the load drops below freezing. Take the water away and the ice bridge has nothing to form from.

Breathability does not cost containment. In Toreto’s own wrap tests — the same pallet, the same machine, the same power stretch and tension settings — Aerosonic and Supersonic at 16µ held 10 kg per square inch on 66 g of film per pallet, against 9.9 kg per square inch on 200 g for 23µ solid film, at roughly €0.32 against €0.48 a pallet. Those are Toreto’s own measurements, and cost per pallet varies with film price and pallet size.

Perforated film is not one product. How much air actually moves through the load depends on how large the holes are and how many there are, and both should be set against the load rather than lifted from a catalogue. Too little open area and the wrap behaves like a solid film in the freezer.

There is a second failure that is harder to see on the roll. Our team’s field experience is that rival perforated films can look identical unrolled and then underperform, because their holes do not open as the film is applied — the film itself will not stretch. Where airflow is the whole point, Aerosonic Lite is built around it: macro-perforated with large aeration holes and reinforcing bands, wrapping in a single layer where competing materials need several.

Yes, and it does not need a different machine. Supersonic and Aerosonic are made from the same materials and perform the same way, so an operation can move between the solid film and the breathable one at the same cost per pallet, on unchanged machine settings. Other breathable films on the market typically cost up to 100% more in use and need settings of their own to perform adequately.

Apply the inside face of the film to the goods; it has the better adhesion. Two revolutions at the base to lock the load onto the pallet, then spiral up with a 20–30 mm overlap, then two revolutions at the top. Tension enough to secure the load fully, but not so much that you crush it. On heavy or slippery loads, spiral back down to the base — the criss-cross adds stability. Finish with a clean cut or a tear.

Then do not undo it. A pallet hood, a second wrap in solid film, a layer of shrink over the top: any of those puts the vapour barrier straight back. The stack is worth a look too — a wrap can only pass the air that the pattern lets through, so cartons butted tight on every face leave the airflow no route in.

Ask for hole size and perforation count set against your load rather than a standard pattern, and ask what happens to those holes when the film is applied under tension. Ask whether your machine settings change, and ask for machine and hand grades if you wrap both ways. Then ask what the film weighs per pallet and what it holds — those two figures together are the only fair comparison.

Do not accept a freezing time from a brochure, including ours. How much faster a load reaches temperature depends on the product, the carton, the stack pattern and how your own cell moves air, so it is measured on your pallets at quotation rather than promised in advance. Ask for a sample, wrap your own load, and run it through your own freezer with the figures written down.