Freezing tunnels are small refrigeration spaces, much longer than the width, completely thermally insulated, intended for bulk or prepacked food, placed in trays, on mobile racks. It is used for quick freezing of meat, fish, dairy and flour products, pastries, fruits and vegetables.
These systems allow a rapid drop in temperature that maintains the quality characteristics of food. The rapid decrease of the temperature up to + 3 ° C in the middle of the product allows to avoid the appearance of bacteria, the main cause of food aging. The rapid cycle of lowering the temperature will keep the freshness of the products both inside and outside.
When thawed, the product will have the same characteristics as a fresh product, without losing weight, freshness or initial organoleptic characteristics.
The air has temperatures of -25 ° C – -40 ° C, and its speed is at least 1.5 m / s without products. The fans ensure a flow rate of at least 150 – 300 recirculations per hour of the empty cell volume.
The duration of the freezing cycle depends on the type of products:
– 2 hours for small pre-packaged products;
– 12 – 18 hours for meat half-carcasses;
– 24 – 40 hours for birds prepackaged in cardboard boxes.10
The problems raised by the sizing of freezing tunnels are:
– The need to cool the product in a certain period of time;
– The need to perform the initial thermal shock;
– Highly variable refrigeration load during the freezing cycle;
– High flow rates of recirculated air;
– Available pressure to fans to penetrate the product mass;
– High humidity releases during freezing.
The products for which freezing tunnels are most often used are:
– Pre-packaged butter in cardboard boxes;
– Bird entrails prepackaged in plastic bags;
– Packages with sliced meat;
– Fish in the form of lighters, etc.