Surströmming



Surströmming ("soured (Baltic) herring") is a northern Swedish delicacy consisting of fermented Baltic herring. Surströmming is sold in cans, which when opened release a strong smell. Because of the smell, the dish is often eaten outdoors. However, opening the can under water somewhat lessens the smell, as well as keeping the person opening it from getting soaked in brine, as the fermentation often builds up a considerable pressure inside the can.

The herring is caught in spring, when it is in prime condition and just about to spawn. The herring are fermented in barrels for one to two months, then tinned where the fermentation continues. Half a year to a year later, gases have built up sufficiently for the once cylindrical tins to bulge into a more rounded shape. These unusual containers of surströmming can be found in supermarkets all over Sweden. However, certain airlines have banned the tins on their flights, considering the pressurized containers to be potentially dangerous. Species of Haloanaerobium 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.

One proposed explanation of the origins of this method of preservation is that it began long ago, when brining food was quite expensive due to the cost of salt. When fermentation was used, just enough salt was required to keep the fish from rotting. The salt raises the osmotic pressure of the brine above the zone where bacteria responsible for rotting (decomposition of proteins) can prosper and prevents decomposition of fish proteins into oligopeptides and amino acids. Instead the osmotic conditions enable the Haloanaerobium bacteria to prosper and decompose the fish glycogen into organic acids, giving it the sour (acidic) properties.

Historically also other fatty fish, like salmon and whitefish, have been fermented not unlike surströmming, and the original gravlax has resembled surströmming.

Eating surströmming
Surströmming is often eaten with a kind of bread known as tunnbröd, literally "thin bread". This thin, either soft or crispy bread (not to be confused with crisp bread) comes in big square sheets. The bread is buttered and then topped with some chopped (usually red) onions and boiled potatoes that have been peeled and sliced. The potatoes are of a special kind, called mandelpotatis or almond potatoes.

A whole fish is forked from the tin and sliced down the middle. Its soft insides are removed, including the dark gray roe, and then the fish is to be opened up like a book. The red flesh is stamped with a fork, loosening the bone and so that it can be filleted. Small pieces are then cut ready for the sandwich. The final touch is a big dollop of gräddfil (fat fermented milk) or sometimes the french equivalent crème fraîche (which is quite similar to gräddfil but even richer in fat). The soft tunnbröd can then be folded or rolled up, while the crispy variety is usually eaten as a sandwich.

The surströmming sandwich is traditionally served with a glass of cold milk and a snaps. As surströmming is both sour-tasting and salty, it induces thirst. Beer has also become popular, although the combined effects of the surströmming and the release of carbon dioxide from the beer can be quite unpleasant for some time after the meal.

Lots of people do not care for surströmming, and it is generally considered to be an acquired taste. Conversely, it is a food which is subject to strong passions (as is lutefisk), and occasionally people like the taste on first try. In May 2005, the first surströmming museum in the world was opened in Skeppsmaln, 30 km north of Örnsköldsvik, a town at the northern end of Höga Kusten ("The High Coast") in north Sweden.

Controversy
In April 2006, several major airlines (such as Air France and British Airways) banned the fish citing that the pressurized cans of fish are potentially explosive. The sale of the fish was subsequently discontinued in Stockholm's international airport. Those who produce the fish have called the airline's decision "culturally illiterate," claiming that it is a "myth that the tinned fish can explode."