Why shrimp stick together in IQF freezing and how to prevent it

Shrimp that clump after freezing are the most expensive defect at the packing table: workers break clusters apart by hand, antennae and tails get damaged, the glaze chips, and a buyer of IQF product may reject the whole lot. This article explains why shrimp stick together, at which stage it happens, and what an IQF freezing line must do to keep every piece separate from start to finish.

Short answer

Shrimp stick together when wet surfaces touch before they have frozen, or when a soft glaze is pushed together before it sets. To keep shrimp separate, the line has to freeze the surface very quickly on entry, keep pieces apart while they freeze, and let each glaze layer harden and re-freeze before the next step.

1. Where does clumping happen?

• At the IQF infeed: freshly washed shrimp carry a lot of surface water. If the belt is loaded too thickly, pieces overlap and the water between them freezes into an ice bridge.
• Inside the freezer: with weak or uneven airflow the surface freezes slowly, and the "sticky" phase lasts longer.
• After glazing: unfrozen glaze water is a strong glue. Freshly glazed shrimp that fall onto each other at a belt transfer will clump.
• In multiple glazing: if the previous layer is not hardened and re-frozen, the next pass partly washes it off and the shrimp stick together.

2. Why does fast freezing keep shrimp separate?

The riskiest moment is the first few dozen seconds, while the surface is still wet. GLORY Thermal Jet® IQF freezers blow high-velocity cold air jets (–40 to –42 °C) straight onto the product from above and below the belt, breaking the warm boundary layer around each shrimp. The surface freezes very quickly, forming a thin hard crust before pieces can stick, and dehydration is reduced.

3. Do shrimp have to be spaced out by hand?

On many lines the only option is to place pieces far apart, which costs labour and capacity. GLORY's patented individual freezing technology, developed on its own patent from 2007, separates shrimp inside the IQF freezer. Product does not need careful spacing: with an inclined infeed conveyor, 3 to 4 people typically feed about 1,000 kg/h of individual shrimp.

4. Keeping shrimp separate through glazing

Separate shrimp at the IQF outlet are only half the job. In a complete shrimp line the product continues through the dipping & spraying glazer, the hardening conveyor and the re-freezer:

• The hardening conveyor lets the glaze set and excess water drain, so free water does not follow the product into the re-freezer.
• The re-freezer hardens the glaze and brings the core to –18 °C, so the glaze does not crack or stick during packing.
• Double or triple glazing: each layer is fully hardened and re-frozen before the next is applied, so earlier layers are not washed off and shrimp do not stick, with a final rate up to about 45%.
• Belt transfers: GLORY's own flighted incline conveyor releases every piece cleanly at the outlet, so cold shrimp do not cling to the belt and drop off on the return side.

5. A quick check of your existing line

• Clumps right at the IQF outlet: check infeed layer thickness, surface water after washing and chamber temperature.
• Separate at the IQF but clumped after glazing: check whether the hardening conveyor and re-freezer give enough dwell time.
• Glazing rate drifting through the shift: are all belt speeds synchronized with the load, or still set by hand on each machine?

The Master AutoCell® control panel sets every belt speed by product, size and load, so outlet temperature and glazing ratio stay on target without operators adjusting each machine.

Frequently asked questions

Do breaded shrimp clump in an IQF freezer?
Breaded products need fast surface freezing so the coating keeps its shape. The M-series mesh belt IQF freezer is widely used for tempura shrimp and Nobashi.

Is flake ice needed in glazing to prevent clumping?
No. The GLORY glazer has a built-in chiller using propylene glycol and adjusts water temperature automatically to the target glazing rate.

How do I find out what my line needs?
Fill in the freezer questionnaire or read the shrimp glazing guide. GLORY engineers will review your product, size and output and propose what to add, for example a glazer and re-freezer for double glazing.