Block Shrimp Thaw: Why the Pad Under a 5 kg Block Stays Dry for Six Hours

A coldstore in Cebu runs 5 kg blocks of black tiger shrimp through a 0 to 2 °C thaw room on a thirty-six hour cycle. The supervisor there keeps a photograph on his phone: a tray at hour one, pad bone dry, block frosted white. A tray at hour fourteen, pad dark and heavy, tray holding fifteen millimetres. Nothing changed in the room. The product simply released its water late, all at once, and the pad had been sitting there doing nothing for most of a shift.

Block frozen shrimp and fish behave nothing like fillets or portions on a pad. This article explains the geometry that delays the drip, what to do with the hours before it arrives, and how to size a pad for a load that discharges its water in a four-hour window.

The Block Is Its Own Insulation

A 5 kg block measuring roughly 400 by 250 by 90 mm has a surface-area-to-volume ratio far lower than a tray of loose fillets. Heat enters through five faces, and the centre of the block stays below -5 °C long after the outer 15 mm has softened. Meltwater from the outer layer cannot escape: it is held in the gap between shrimp by capillary action and surface tension, and by the glaze that was sprayed on at packing.

Thaw time for a block of that size at 2 °C air is typically thirty to forty hours without forced air, and eighteen to twenty-four with it. Drip does not arrive steadily across those hours. It arrives in a burst once the block has lost structural coherence, usually between hour eight and hour sixteen depending on air speed and stacking.

Glaze Is Water You Are Also Paying to Absorb

Export blocks usually carry a protective glaze of 8 to 12 percent of net weight. On a 5 kg block that is 400 to 600 grams of water that will melt before any tissue fluid does, and it will arrive at the pad first, at low temperature and low viscosity. A pad sized only for the shrimp drip will be half spent before the real load begins.

Buyers who specify pad grammage against net product weight alone therefore under-order. The working rule for glazed block product is to add the glaze percentage to the drip estimate before selecting a pad, then add a 20 percent margin for the burst.

Standoff, Rack Angle and the Contact Problem

A block sitting flat on a pad touches it across one face, and that face is the coldest and the last to release water. Drip runs down the block sides, bypasses the pad edge, and lands directly on the tray floor. This is the single most common reason a correctly sized pad still leaves a wet tray.

Three fixes work, alone or together. Elevate the block on a 10 mm perforated standoff so liquid falls through rather than pooling at the contact face. Tilt the tray 3 to 5 degrees toward a pad, so runoff crosses the absorbent rather than the bare tray. Or wrap the block loosely in a perforated liner that wicks to the pad at four points. The standoff costs the least and changes the outcome most.

Changing the Pad on a Burst, Not a Schedule

A twelve-hour change interval is wrong for block product in both directions. It wastes pads during the dry first six hours and it misses the burst. The schedule that works is two-stage: a light pad, 150 to 200 gsm, for the first eight hours to catch glaze and condensation, then a heavy pad, 400 to 500 gsm, fitted when the block begins to yield under thumb pressure at the corner.

That trigger is teachable in a five-minute briefing and needs no instrument. Line staff press a corner of the block; when it gives, the pad gets changed. On a thirty-six hour cycle this lands at two changes instead of three, and the tray stays dry through the burst.

Block product is where pad reserve capacity matters most, because the load is not spread across the shift. Our SAP absorbent media for block and bulk thaw are graded by retained capacity under load, which is the figure that decides whether the burst is contained.