Freezing Technology

4.1.1.4 Choice of method

Many factors should be considered when choosing between the various methods. The choice depends largely on the type of product and the form in which it was frozen. In some uses, it is difficult to provide sufficient shielding in the dielectric thawer. The air-blast thawer might be at a disadvantage in the amount of cleaning required to keep bacterial counts within the statutory limits. All the main methods described above can produce satisfactory results with blocks of whole fish. Both heat conduction and electric methods fail with large fish. The electric methods give more uniform thawing with compact block at small fish. 'Continuous thawers’ would appear to have advantage over batch thawers for blocks at whole fish. For blocks of fillets, water thawing is unsuitable and block thickness probably should not exceed 5 cm for thawing in humid air blast and between heated plates. The electric methods give good results with blocks of fillets. Block upto 10cm thick have been thawed successfully dielectric thawer using only three generators. Fillets, unprotected by the skin of the fish, are more susceptible than whole fish to deterioration on thawing, particularly shrinkage, discolouration and dehydration. Pronounced thaw-rigor accompanied by shrinkage and loss of fluid sometimes can be produced when thawing is rapid.