Plate freezer
Also known as: contact freezer, contact plate freezer
Short definitionA machine that freezes product by contact, pressed between metal plates with refrigerant flowing inside them. It freezes regular-shaped blocks faster and with less energy than air blast freezing.
Refrigerant evaporates at −35 to −40 °C inside channelled aluminium plates. The product is placed between two plates, a hydraulic system presses the plates lightly, and heat passes straight into the metal from both faces. There are no fans. In the horizontal type, trays or cartons are loaded between the plates; it is used for blocks of fillets, shrimp and minced meat. In the vertical type, whole fish and offal are poured into the stations from above and come out as unwrapped blocks.
Block thickness drives the selection. It ranges from 25 to 100 mm and the time grows almost with the square of the thickness; a 50 mm block reaches −18 °C at the core in about 1.5–2 hours. If the product does not sit fully against the plate, the tray is half full or the packaging bulges, the time gets longer. The low evaporating temperature calls for a two-stage, economised screw or CO₂ cascade system. Irregular-shaped product does not suit this machine and is frozen with air.