IQF Continuous Immersion ultra-freezing uses a solution of salt (sodium chloride), the fish moves through several tanks filled with the brine at -20ºC until it reaches the desirable freezing state. Immersion in sodium chloride brine was one of the very first methods used to freeze fish since it was a logical progression from the method used to freeze block ice. By using a liquid for the removal of heat from the fish product, favourable freezing rates can be achieved. Liquid can remove more heat per unit volume than gas (eg. air).
This technique is used mostly for the canning industry fish where the little salt that is absorbed is not detrimental to the canned product since salt is usually added to the product before canning in any case.