Proper thawing prolongs freshness of frozen fish

The fish should be frozen on board the vessel and thawed properly before it reaches the marketplace, the study says.

The thawing tests, performed on codfish, explored how to achieve the best possible quality after freezing and subsequent thawing.

Dubbed Qualifish, the project was led by SINTEF (The Foundation for Scientific and Industrial Research) Norwayin collaboration with the Norwegian Institute of Nutrition and Seafood Research and the Icelandic research institute Matís.

The researchers carried out tests to examine the effect of different thawing methods and the results of these methods on the quality and shelf-life of cod, a seasonal fish.

After thawing, laboratory tests indicated the quality of fish continued to be good for as long as 10 days in terms of texture, color, airiness, being bacteria-free and having “top quality” consistency of flesh.

Three factors are essential to these achieving these results.

First, fish must be frozen before rigor mortis sets in, meaning the process has to be done on board the vessel.

Afterwards, the fish must remain frozen at a stable and low temperature leading up to thawing and there must be no interruptions in the “cooling chain.” Fish could be thawed slowly at between 0.5 to 10°C for up to 28 hours.

“Thawing itself must then take place immediately before the fish are put on sale, and carried out in water under controlled conditions. If air bubbles are added to the water, the quality of the cod will be even better,” says the study.

The negative connotation of “frozen fish” could be traced to the freezing equipment in the early days, which expanded water in the cell membranes of the fish, making it mushy. Latest freezing technology allows a very fast process that does not leave time for the ice crystals to form.

In the US, the Food and Drug Administration’s Food Code recommends freezing as a method of killing parasites.