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Cryogenic Freezing and Chilling
The chilling and freezing process may be seen as a lowering of the product temperature from its original value to the required storage temperature.
The term 'chilled foods' is used to describe food items where the product temperature has been reduced to any temperature above freezing point.
The freezing process
The freezing process can be divided into three phases:
- pre-freezing
- freezing
- lowering of the temperature to the required storage temperature - typically below -10°C
Heat must be moved from the interior of the product to the surface by conduction. The heat can be removed from the surface of the product by direct contact with a cryogenic liquid such as liquid nitrogen or carbon dioxide snow.
Required freezing time
The required freezing time depends on a number of factors, the most important of which are:
- the dimension and shape of the product
- the thermal properties
- initial and final temperatures
- the temperature of the cryogenic liquid or solid
- the coefficient of heat transfer
Benefits
Chilling a food product reduces the risk of bacterial growth. Rapidly chilling a product with liquid nitrogen or carbon dioxide snow results in greater risk reduction.
When a product is frozen, ice crystals are formed. Only at very rapid cryogenic freezing rates are small crystals formed uniformly throughout the tissue, both inside and outside the cells.
The importance of the size of the ice crystal has long been regarded as crucial for the quality of the frozen product.
When the temperature is lowered below the freezing point, the growth of micro-organisms decreases rapidly, and will completely cease at a certain temperature. This is due not only to the lowering of the product temperature, but also to the formation of ice which reduces the available water necessary for the metabolism of the micro-organisms.
Our capabilities
The Cryoline range offers the ability to:
- cool and freeze products on a batch or continuous production basis
- crust freeze products for slicing-yield improvements
- cool batch products for forming
- cool or freeze sticky or marinaded products with negligible coating loss
