Both methods end at the same temperature; the difference is how long the product takes to get there. Most of the water in food turns to ice between -1 and -4 °C, a band known as the zone of maximum ice crystal formation. Pass through it quickly and the water spreads into many small crystals; pass through slowly and a few crystals have time to grow large.
| Aspect | Slow freezing | Blast freezing |
|---|---|---|
| Crystals | Few and large | Many and small |
| Cell structure | Torn by large crystals | Largely preserved |
| On thawing | Water on the plate, slack texture, weight loss | Less drip, fuller texture |
The Turkish Food Codex Communiqué on Quick-Frozen Foods (2014/47, drawn from EU Directive 89/108/EEC) builds its definition on the same idea: the zone of maximum crystallisation is crossed as rapidly as possible, and after thermal stabilisation the product is held at -18 °C or colder. What makes it blast freezing is the speed through that zone, not the cabinet setpoint. Products high in water with delicate structure gain most: meat, fish, fruit, prepared meals. In dry or structurally robust products the gain shrinks.
A blast cabinet is not a store
Once blast frozen, product moves to a store at -18 °C or colder. Temperature swings in storage slowly enlarge the small crystals, so the gain from blast freezing only lasts with steady storage. A batch left in the blast cabinet wastes energy and holds up the next one; if that next batch waits at room temperature meanwhile, the gain is lost before freezing even starts. Overloading the cabinet also slows freezing, so batch size is planned to the cabinet's capacity.