4.1.1.2 Water thawing

4.1.1.2 Water thawing

a)      Immersion:

The thawing of blocks of whole in water has been shown to give good results, but has been used only to a limited extent for thawing on a large scale. The thawed product can be as high in overall quality and suitable for processing.  Pump capacities for water thawers need not be great, because the water velocity required for good heat transfer is 0.5 cm/sec, giving thawing rates equal to those for air-blast.  It is probably necessary, to use somewhat higher velocities, perhaps 2cm/sec or more, in order to give a good degree of mixing of the water, preventing stratification and to provide reasonably quick response to the heater, particularly for warm up with initially cold water.  Too high velocities induce turbulence, causing foaming at the surface of the water and possibly lead to water logging. The temperature of the water should conserve heat, it is better to change the water once or twice in 24 hour so as to limit the degree of contamination of the water.  

b)      Spray:  

In this, larger thawers are used, in which heated water is sprayed directly on the fish.  The blocks of fish travel on a conveyor, which is made up of a series of open mesh, wire baskets in a housing ventilated by a small fan.  The water is recirculated through a special filter and cleaner section.  The thawing time is claimed to be at least as short as in air, blast thawing.   Hygienic condition is maintained in the thawers because of the working action of the sprays of clean water. It takes about 5 hours for the 10cm block of whole fish to be thawed completely, in a thawer with are output of 1ton/hour. 

Last modified: Saturday, 24 December 2011, 11:31 AM