This chapter describes the principles and methods of the fish thawing process, as well as the thawing systems' structure, functioning, and development. A new method for calculating the duration of food thawing is introduced. The author shares best practices from the refrigeration industry of Russia and developed countries as well as his own experience. He hopes it may help scientists to choose research topics in the field of food freezing. The chapter is meant for students, post-graduate students, and experts working in the field of refrigeration production.
TopThawing Methods
Thawing is conversion of ice contained in frozen fish tissue into water. The process requires energy, usually heat.
The medium that transmits heat to fish is called the processing medium. Air, water and water steam are commonly used as the processing medium.
Depending on the type of energy used, there are thermal and electrical methods of thawing. When using thermal methods, the heat from the processing medium is transferred to the product surface. Thawing is gradual: the surface of fish thaws first, and then the inner layers. This method is also referred to as surface heating thawing.
Electrical thawing methods are based on the electrical properties of fish. Frozen fish is a weak conductor and a dielectric, therefore, for electrical thawing, fish is either connected to the electrical circuit as a conductor or placed in an alternating high frequency electric field and is warmed up as a dielectric. This method is also referred to as volumetric heating thawing.
Thawing in contact with heated plates or by heat (infrared) radiation is not used industrially as it causes the formation of bubbles under skin.