Having frozen the product – either at sea or on land, in horizontal or vertical plate freezers, or less common probably in air blast tunnels – the product is then transported across country or from one continent to another.
Thawing is then required for further processing, for cooking or sale as wet fish for instance
Thawing is basically a reversal of the freezing process, but suffers from two problems that do not occur in the freezing process.
a. During freezing, surface temperatures are rapidly lowered and the rate of bacterial growth reduces drastically at freezing temperatures.
In thawing the surface is the first to rise in temperature and bacterial growth can recommence.
On large objects subject to long uncontrolled thawing cycles surface spoilage can occur before the centre has been fully thawed.
b. Second problem is that the thermal conductivity of water is one third that of ice. Consequently head conduction through a thawed outer surface into the frozen inner regions is far more difficult than through the frozen surface layers in the freezing process.
A substantial majority of commercial thawing systems rely on the conduction of head through the surface of the product and the microbiological requirement to maintain low surface temperatures combined with the poor conductivity results in long thawing cycles
Modern thawing systems can be divided into two different categories depending on whether heat is conducted into the product via its surface or generated electromagnetically inside the produce i.e. volumetric heating. Frozen food suplliers in Melbourne has the advance technology in terms of producing high quality frozen products.
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