Fermented fish are among the Scandinavian delicatessen even if… it takes some effort to appreciate it, as it surely is an ‘aquired taste’ — to say the least. We are talking about the Swedish Surströmming (or sour herring), the Icelandic Hákarl (or fermented shark), and the Norwegian Rakfisk (or moist/soaked fish, usually trout or char).
An old staple in European cuisines, the oldest archeological findings of fish fermentation are 9,200 years old, from the south of Sweden, but more recent examples include garum, a fermented fish sauce made by the ancient Greeks and Romans, and Worcestershire sauce, which also has a fermented fish ingredient. Preservation of fish through fermentation in a weak brine may have developed when brining was still expensive due to the cost of salt. In modern times, the fish are initially marinated in a strong brine solution that draws out the blood, and then fermented in a weaker brine in barrels prior to canning — which from the 19th century onwards enabled the product to be marketed in shops (also farther south in Sweden) and stored at home. The fermentation happens through autolysis: it starts from a lactic acid enzyme in the spine of the fish and, together with bacteria, pungent smelling acids and Hydrogen sulfide are formed. The salt raises the osmotic pressure of the brine and prevents decomposition of proteins: the osmotic conditions enable Halanaerobium bacteria to decompose the fish glycogen into organic acids, making it sour (acidic).
Surströmming is a lightly-salted fermented Baltic Sea herring (smaller than the Atlantic herring, found in the North Sea) traditional to Swedish cuisine since at least the 16th century. During its production, just enough salt is used to prevent the raw herring from rotting while allowing it to ferment: at least six months of fermentation process gives the fish its characteristic strong smell and somewhat acidic taste, actually one of the most putrid food smells in the world. At the end of the 1940s surströmming producers in Sweden lobbied to prevent incompletely fermented fish from being sold: the decree forbade sales of the current year’s production in Sweden prior to the third Thursday in August and retailers still today maintain the date for the “premiere” of that year’s catch.
Hákarl (referred to as fermented shark in English) is an Icelandic national dish consisting of a Greenland or other sleeper shark treated with a particular fermentation process and hung to dry for four-five months. Available in Icelandic stores all year-round, it has a strong ammonia-rich smell (similar to many cleaning products) and fishy taste, but is most often served in cubes on toothpicks as part of a selection of traditional Icelandic food called þorramatur served at the midwinter festival þorrablót. Hákarl is often eaten with a shot of brennivín, the local spirit (a type of akvavit) and it comes in two varieties: the chewy and reddish glerhákarl from the belly, or the white and soft skyrhákarl from the body.
Rakfisk is a Norwegian fish dish made from trout or char, salted and autolyzed for two-three months, up to a year. Rakfisk is eaten without cooking and has a mild and slightly salty flavor and strong smell. The first record of the term rakfisk dates back to 1348, but the history of this food is probably even older, although no sources are available as to its exact invention year. Fisk is the Norwegian for “fish”, whereas Rak derives from the word rakr, meaning “moist” or “soaked” in Norse language. Rakfisk is made from fresh trout or char: after gutting and rinsing it, the fish is placed in a bucket and salted (small amounts of sugar may be added). The fish is then placed under pressure with a lid that fits down into the bucket and a weight on top: a brine is formed as the salt draws moisture from the fish. The rakfisk bucket is stored at under 5 degrees Celsius for one to three months. The finished product does not need cooking: Rakfisk is traditionally served sliced or as a fillet on flatbrød or lefse and almond potatoes. Some also use raw onion, sour cream, mustard-sauce, a mild form of mustard with dill.