Surströmming (pronounced [ˈsʉ̂ːˌʂʈrœmːɪŋ]; Swedish for 'sour herring') is a lightly salted, fermented Baltic Sea herring traditional to Swedish cuisine since at least the 16th century. It is distinct from fried or pickled herring. The Baltic herring, known as strömming in Swedish, is smaller than the Atlantic herring found in the North Sea. Traditionally, strömming is defined as herring caught in the brackish waters of the Baltic north of the Kalmar Strait. The herring used for surströmming are caught prior to spawning in April and May. During the production of surströmming, just enough salt is used to prevent the raw herring from rotting while allowing it to ferment. A fermentation process of at least six months gives the fish its characteristic strong smell and somewhat acidic taste. A newly opened can of surströmming has one of the most putrid food smells in the world, even stronger than similarly fermented fish dishes such as the Korean hongeo-hoe, the Japanese kusaya or the Icelandic hákarl, making surströmming an acquired taste. At the end of the 1940s, surströmming producers in Sweden lobbied for a royal ordinance (Swedish: förordning) that would prevent incompletely fermented fish from being sold. The decree that was issued forbade sales of the current year's production in Sweden prior to the third Thursday in August. While the ordinance is no longer in force, retailers still maintain the date for the "premiere" of that year's catch.
Origin Surströmming has been part of northern Swedish cuisine since at least the 16th century. Fermented fish is a traditional staple in European cuisines. The oldest archeological finds of fish fermentation are 9,200 years old and originate from the south of today's Sweden. More recent examples include garum, a fermented fish sauce made by the ancient Greeks and Romans, and Worcestershire sauce, which also contains fermented fish. Preservation of fish through fermentation in 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, then fermented in a weaker brine in barrels prior to canning. The canning procedure, introduced in the 19th century, enabled the product to be marketed in shops and stored at home, whereas formerly the final stage would have been stored in large wooden barrels and smaller, one-litre kegs. Canning also enabled the product to be marketed farther south in Sweden.
Chemical process Fermentation occurs through autolysis and starts from a lactic acid enzyme in the spine of the fish. Together with bacteria, pungent smelling acids are formed, such as propionic acid, butyric acid and acetic acid. Hydrogen sulfide is also produced. The salt raises the osmotic pressure of the brine above the zone where bacteria responsible for rotting can thrive and prevents decomposition of proteins into oligopeptides and amino acids. Instead, the osmotic conditions enable Halanaerobium bacteria such as H. praevalens to thrive and decompose the fish glycogen into organic acids, making it sour (acidic).
Production and market
The herring are caught in May and June, when they are in prime condition and about to spawn, and have not yet fattened. They are put into a strong brine for about 20 hours that draws out the blood, after which the heads and innards are removed and the fish is put into a weaker brine solution. The barrels are placed in a temperature-controlled room kept at 15–18 °C (59–64 °F). Canning takes place at the beginning of July and for three to four weeks thereafter. Ten days prior to the premiere the final product is distributed to wholesalers. The fermentation of the fish relies on a lactic acid enzyme in the spine that is activated if the conditions, temperature and brine concentration, are right. The low temperature in Northern Sweden is one of the elements that contribute to the character of the final product. Prior to the development of modern canning methods, surströmming was sold in wooden barrels for immediate consumption, as even the smaller kegs could leak. Fermentation continues in the can, causing it to bulge noticeably, which would usually be a sign of botulism or other food poisoning concern in non-fermented canned foods. Species of Halanaerobium bacteria are responsible for the in-can ripening. These bacteria produce carbon dioxide and a number of compounds that account for the unique odor: pungent (propionic acid), rotten-egg (hydrogen sulfide), rancid-butter (butyric acid), and vinegary (acetic acid). Due to these gases, a thousand cans of surströmming exploded over a period of six hours during a fire at a Swedish warehouse in 2014. Surströmming is commonly sold in grocery stores all over Sweden. According to the Surströmming Academy's statistics from 2009, about 2 million people eat surströmming annually. Sweden's export of surströmming is only 0.2 percent of all produced surströmming. Many people do not care for surströmming. As with the Nordic dried-fish dish lutefisk, it is a food that meets strong reactions. It is more popular in northern Sweden than in other parts of the country. As of 2023, over the past few years, the supply of Baltic and other herring caught by Swedish fishermen has dramatically declined. Baltic herring fisheries have been used unsustainably since the Middle Ages, and overfishing is pushing populations to the brink of collapse. With such low catch numbers, retailers are now selling out their entire supply within minutes of the annual surströmming release.
Preparation
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