Stockfish is unsalted fish, especially cod, dried by cold air and wind on wooden racks on the foreshore, called “hjell”. The drying of food is the world’s oldest known preservation method, and dried fish has a storage life of several years. The method is cheap and effective in suitable climates; the work can be done by the fisherman and family, and the resulting product is easily transported to market.
Cod is the most common fish used in stockfish production, while other whitefish, such as pollock, haddock, ling and cusk, are used to a lesser degree.
Over the centuries, several variants of dried fish have evolved. The stockfish (fresh dried, not salted) category is often wrongly mixed with the clipfish, or salted cod, category where the fish is salted before drying. After 2–3 weeks in salt the fish has salt-matured, and is transformed from wet salted fish to clipfish through a drying process. The salted fish was earlier dried on rocks (clips) on the foreshore. The production method of clipfish was developed by the Portuguese who first mined salt near the brackish water of Aveiro, and brought it to Newfoundland where cod (bacalhau) was available in massive quantities. Salting was not economically feasible until the 17th century, when cheap salt from southern Europe became available to the maritime nations of northern Europe.
Stockfish is cured in a process called fermentation where cold-adapted bacteria matures the fish, similar to the maturing process of cheese. Clipfish is processed in a chemically curing process called salt-maturing, similar to the maturing processes of other salt-matured products like Parma ham.