Blast freezing
Also known as: quick freezing, shock freezing
Short definitionFreezing a product within a few hours under very cold, fast-moving air. The ice crystals stay small, so texture and flavour are preserved.
Most of the water in food turns to ice between −1 and −5 °C. If the product lingers in this range, the crystals grow and tear the cells; it then loses water when thawed. Blast freezing gets through this range quickly. Air blast rooms and tunnels are the most common route; IQF is used for small pieces, plate freezers for fish blocks and liquid nitrogen for very fast jobs.
A blast freezer quote starts with three questions: how many kilos go in per day, at what temperature the product enters and leaves, and in how many hours it must freeze. Thickness and packaging set the time; a thin piece freezes in a few hours, a thick carcass cut takes a day, and cartons add to it. The load is the sum of sensible heat above freezing, latent heat and sensible heat below freezing. A storage room’s capacity cannot do blast freezing.