Every frozen seafood specification has to answer one question: are the pieces frozen individually, or frozen together in a solid mass? It sounds like a technicality. It is not — it changes the price, the handling, the thaw loss and, ultimately, who can use the product.
What each method actually is
IQF — individually quick frozen. Pieces pass through a blast tunnel or spiral freezer on a belt, freezing separately at high air velocity in minutes. They stay separate in the bag. The end user pours out what they need and returns the rest.
Block frozen. Product is packed into a pan, usually with water, and frozen as a solid 10 kg or 20 kg slab. It arrives as one piece. To use any of it, you thaw all of it — or you saw it.
Head to head
| Factor | IQF | Block frozen |
|---|---|---|
| Cost per kg | Higher — slower line, more energy, more packaging | Lower — the cheapest way to freeze volume |
| Portioning | Take what you need, refreeze nothing | All or nothing per block |
| Ice crystal size | Small — faster freeze, better cell structure | Larger at the block centre — slower freeze |
| Thaw / drip loss | Lower, if handled properly | Higher, especially from the block core |
| Freezer burn risk | Higher — more surface area exposed; glazing mitigates it | Very low — the ice matrix seals the product |
| Long transit tolerance | Good with adequate glaze | Excellent |
| Best channel | Retail packs, food service, ready meals | Processors, re-packers, industrial lines |
| Glazing | Applied per piece, declared as a % | Effectively the freezing water; state net vs gross |
The decision, in one paragraph
If the person who opens the pack is a cook or a consumer, buy IQF. If the person who opens the pack is going to thaw and re-work the whole thing anyway — a processing line, a re-packer, a surimi plant — buy block and keep the difference. That is genuinely most of the decision.
Where block frozen still wins on quality
There is a common assumption that IQF is simply the better product. On a long ocean transit with imperfect temperature control, that is not always true. A block is a sealed ice matrix: almost no product surface is exposed to air, so freezer burn and oxidative rancidity are far slower. IQF pieces have enormous surface area, and the only thing standing between them and dehydration is the glaze. Under-glazed IQF on a five-week transit through a warm reefer cycle will look worse on arrival than block frozen product from the same catch.
This is why glazing percentage belongs in the specification, not in a footnote. And why it must be stated separately from net weight — otherwise you are buying water at seafood prices. The shrimp size chart post works through what that costs.
By product type
- Shrimp — IQF for retail and food service; block for processors. Both are standard from India. See the shrimp page.
- Squid and cuttlefish — whole round almost always block; whole cleaned, rings and tentacles almost always IQF. See cephalopods.
- Small pelagics (Indian mackerel, ribbon fish, threadfin bream) — block is the norm, both on cost and because most of it is re-processed.
- Premium fin fish (pomfret, grouper, snapper, seer fish, tuna) — IQF, because the buyer is looking at the individual fish. See fin fish.
- Value-added and retail-ready — IQF by definition. See value-added seafood.
What to write on the order
State the freezing method, the glazing percentage, the interleaving (for blocks), the inner pack and the master carton weight. And state that price is on net weight. Four extra words on a purchase order have saved more money in this trade than most negotiations.