Methods for (industrial) thawing of fish blocks: A review

The food processing industry is facing challenges when it comes to the thawing of fish and fish products. These challenges include most importantly the quality of the product to be thawed, the profitability of the operation and to some minor degree the environmental impact of the whole operation. Without doubt, thawing (and freezing) has a large impact on the structure and other quality factors of fish. In addition, both serve as bottlenecks in the production chain with direct effects on the profitability and hence also on the environment, for example, if the thawing process takes longer than necessary, energy is wasted and the quality of the product might suffer. In this concise review, several methods for (industrial) thawing of fish are presented and discussed, mainly with respect to their technical specifications and functional principles. These methods can be divided into two main principal types, namely the ones that provide heat to the frozen fish only via its boundary layers, and the ones that generate heat also in the frozen fish's inner spatial domain. Both types come with advantages and disadvantages; however, the latter types are generally not (yet) suitable for industrial large-scale operation. The theory, functional principles and advantages/disadvantages will be highlighted in this work. In addition, an outlook on future developments as well as proposals for further research will be provided. Practical applicationsThawing of fish is a very important step in the production chain from catch to salable product. Freezing serves both as shelf-life extension for large catches and as a possibility to dampen out seasonal fluctuations of different species to make them available all year round. However, a frozen headed and gutted fish cannot be processed further (e.g., filleted), it has to be thawed to perform further processing of the product.