A common food dish of Norway, Sweden and parts of Finland, made from whitefish, usually cod, soaked in water and lye (caustic soda) prior to cooking, using a process referred to a "luting" which served to dry the filet so it could be preserved. During earlier times, potash was used instead of lye. The whole or cut pieces of the cod were placed in a tub filled with cold water changed daily and allowed to remain in a cold area for approximately a week. After a week, lye was added to the water and again the fish was kept in the solution for 4 days, during which time it began to swell in size as half the protein in the fish is removed. At this point the meat of the fish is poisonous and cannot be eaten, so it is then washed with cold water and placed in a bath containing only water for another 4 to 5 days to remove the lye. The steeping and bathing of the fish filets as well as the loss of protein, which continues as the filets are washed prior to preparing, results in a clear, gelatin-like appearance and texture to the cod meat. It is the lye which contains an alkali solution that causes the reaction to occur so the meat of the fish takes on a clear, translucent appearance. As Scandinavians moved to other countries, it became a tradition for them to serve Lutefish on holidays and for family celebrations as a means to retain the heritage of their popular food dish.
Served as a main dish, Lutefisk was traditionally prepared by boiling the filets in a kettle of water mixed with a little salt. A topping of butter or creamed gravy was often added to the fish that was then served with boiled or mashed potatoes, meatballs, goat cheese such as geitost, lefse, and flatbreads. Cod is the fish generally associated with Lutefisk, but other varieties of whitefish were also used to make this dish, such as ling (a type of cod) and pollack.