Vacuum-Packed Portions: What the Pad Is Actually There For

“The pads come off the line bone dry,” the production manager said, tapping a stack of 5 kg packs. “So we are paying for nothing.” He was running 400 vacuum packs a day through a 4 °C thaw room, and every sheet underneath came up clean. It took one rejected consignment six weeks later to change his mind.

He was reading the pad as an absorbent. Under a sealed pack it is not one, at least not for the product. It is doing three smaller jobs, and two of them only matter on the day something goes wrong.

Job one: catching what the bag is not holding

A vacuum pack is a barrier until it is not. Seals fail at the shoulder of the bag, at a wrinkle left by a product corner, or where a bone has nicked the film during boxing. Industry leak rates on formed packs commonly sit between one in 200 and one in 500, and most of them are slow: a few millilitres an hour, invisible at the pack, obvious on the carton twelve hours later.

With a pad under the pack, that leak lands in a defined footprint. The sheet goes damp, dark and heavy in one spot while its neighbours stay dry. That is a locating tool. Without it, the first evidence is a stained carton in the cold store or, worse, a customer complaint about a bloated pack in a delivery.

Job two: the water that arrives from outside the pack

Packs come out of a blast freezer at -18 °C and go into a room at 3 °C. Condensation forms on the film within minutes, runs down the outside of the bag and pools in the bottom of the crate. Add ice glaze shedding off the pack surface and you have 50 to 150 ml per crate of liquid that has nothing to do with the product.

Left alone, that water softens the corrugated crate, lifts the print off the label, and makes the whole consignment look mishandled to whoever opens the door. A 150 to 200 gsm sheet handles the condensate load comfortably. Anything above 300 gsm is money spent on capacity the job never uses.

Job three: cushioning, which nobody writes down

Portions in a 5 kg pack press hard on the corners of the one below. A sheet of airlaid between layers spreads that load and stops the film from creasing against the crate base. In practice this is what saves the seal on the bottom pack of a stack, and it is the reason packing lines that “save” on pads start seeing corner leakers within a month.

The counter-intuitive part

A saturated pad under a sealed pack is not a pad failure. It is almost always a seal failure. Once you accept that, the pad becomes a check rather than a cost: at the end of a thaw, one wet sheet in a pallet of dry ones points at a specific pack, and the pack can be opened, checked and repacked before it ships.

The plant above pulled pads to save 0.19 a pack, about 76 a day. Three weeks later a slow leaker went unnoticed through the whole thaw, the carton collapsed and 24 packs were rejected at goods-in with the delivery docket. The pad would have shown the problem at hour six.

The crate matters as much as the sheet. Corrugated board will wick through its own thickness in about six hours once the sheet underneath is saturated at one corner, and the pallet below then carries the stain. A sheet that stops 10 mm short of the crate wall is not a compromise; it keeps the wetted area away from the corrugation that would otherwise pull water up the side. More consignments are rejected for crate wicking than for seal failures, and the two look identical on a photograph.

If a pallet is going straight to a customer, put a slip sheet of plain liner board between the crate and the pad, and check the bottom layer by hand before the pallet is wrapped. It takes four minutes and it catches the one pack in four hundred that the pad has been quietly flagging all night.

Practical setup for a vacuum-pack room: one sheet per layer, 150-200 gsm, sheet cut to the crate floor so no edge climbs the wall; inspect at the end of each thaw and log any sheet that comes up wet with the pack number beside it. The leak protocol that follows is worth more than the absorbency spec. For plants moving into high-SAP sheets for wet product, the SAP powder grades are a different conversation with different numbers, and mixing the two jobs on one purchase order is where most specification errors start.