Fresh fish rapidly deteriorates unless some way can be found to preserve it. Drying is a method of food preservation that works by removing water from the food, which inhibits the growth of microorganisms. Open air drying using sun and wind has been practiced since ancient times to preserve food. Water is usually removed by evaporation (air drying, sun drying, smoking or wind drying) but, in the case of freeze-drying, food is first frozen and then the water is removed by sublimation. Bacteria, yeasts and molds need the water in the food to grow, and drying effectively prevents them from surviving in the food. Fish are preserved through such traditional methods as drying, smoking and salting. The oldest traditional way of preserving fish was to let the wind and sun dry it. Drying 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. Types Stockfish Stockfish is unsalted fish, especially cod, dried by cold air and wind on wooden racks on the foreshore. The drying racks are known as fish flakes. Cod is the most common fish used in stockfish production, though other whitefish, such as pollock, haddock, ling and tusk, are also used. Clipfish Over the centuries, several variants of dried fish have evolved. Stockfish, dried as fresh fish and not salted, is often confused with clipfish, where the fish is salted before drying. After 2–3 weeks in salt the fish has saltmatured, 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 (or Bacalhau in Portuguese) was developed by the Portuguese who first mined salt near the brackish water of Aveiro, and brought it to Newfoundland where cod was available in massive quantities. (q.v.). 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 saltmaturing, similar to the maturing processes of other saltmatured products like the Parma