A 12 kg Tuna Loin and the Weight Limit of One Sheet

A 12 kg yellowfin loin lands on a 1/1 tray with a 400 gsm sheet under it, and the first thing it does is press. The contact area is roughly 200 by 250 mm, so 12 kg is bearing on 500 cm² — about 24 g/cm², five times the load of a spread-out tray of portions. The sheet is not short of capacity. It is being squeezed.

Whole loins, bone-in legs and large primals break the assumptions that pad sizing is built on, because a single item concentrates weight in a way that a tray of steaks never does.

What pressure does to a wet sheet

An airlaid sheet holds water in the void space between fibres and in the swollen polymer. Under 24 g/cm² the fibre structure compresses by 30 to 50 percent, and the water that was in those voids is pushed sideways out of the contact zone. It does not disappear; it migrates to the perimeter and sits there, under the edge of the loin, where it is in contact with the product and cannot be reabsorbed.

So the pad ends up dry where it is needed and wet where it is not. Lift a loin after 20 hours on a compressed sheet and you will find a dry rectangle in the middle and a dark ring around it. That ring is the failure.

Where the limit sits

For a single item on a 300 gsm sheet, things hold up to about 8 kg on a 300 by 200 mm footprint. Above that, compression starts to cost measurable capacity. At 12 kg on a small footprint, the practical options are:

• Two sheets, staggered: spreads the load and doubles the perimeter, but only helps if the top sheet is offset, not stacked exactly.
• 500 gsm: more loft to lose before the structure closes, but still compresses at 24 g/cm².
• A rack in the tray: the loin sits above the sheet, drip falls through, and the sheet is never loaded mechanically. This is the answer that actually works.

The counter-intuitive finding

In a side-by-side test on two 12 kg loins, the one on a doubled 300 gsm pad lost 1.9 percent of weight and the one on a rack over a single 300 gsm pad lost 1.6 percent — but the doubled-pad loin had a 40 mm wet band along one edge where the run-off collected, and that band was rejected at portioning. The pad that held more water produced the worse outcome, because it held it in the wrong place.

Weight loss on the scale is not the measure. Distribution of the remaining water is.

Practical setup for heavy single items

A stainless rack or a perforated insert 25 mm above the tray floor, sheet below it, product on the rack. The sheet never sees the load, so a 300 gsm is enough for 12 kg. If a rack is impossible, put the loin on two sheets with the top one offset by 100 mm and rotate the loin at the twelve-hour mark, which redistributes the contact patch.

After the thaw, before the saw

A loin that has sat on a compressed sheet comes off the tray with a wet band along one edge, and that band behaves differently on the band saw: it smears, the cut face looks dull, and the portion weights drift. Portioning yield on the first ten slices will run half a percent low, which on a 12 kg loin is 60 g of trim that gets blamed on the saw blade.

Pat the contact face dry before it goes to the saw, and let the loin rest ten minutes at room temperature if the schedule allows. The surface firms, the cut is cleaner, and the portion weights settle. It is a small step that recovers most of what the pad could not.

For heavy single items the question is usually how the high-capacity pad cores behave under load rather than how much they hold in a bath, and that is worth asking before a pallet is ordered.

And weigh it. A 12 kg loin at 2 percent is 240 ml, which sounds small for the sheet size, and that is exactly why the failure gets missed: the volume is modest and the damage is mechanical.