The original treatment of whitefish, particularly cod, was to dry it, in which form it is called stockfish. The water content is reduced to less than a fifth so that the ratio of dried to fresh fish is 5 times. As salt became more readily available the practice changed and the fish was only partially dried before being coated in salt. The ratio of fresh to dry weight of salt cod is only about 3½.
Large amounts of salt cod are produced particularly by Newfoundland in Canada, Norway and Iceland and much is exported to Portugal, where it is extremely popular, France, Spain and Italy.
Salt cod is much eaten during Lent in Catholic countries, it must be soaked for 24 hours or more before use, with occasional changes of water. It can often be purchased ready soaked on Fridays.