Surströmming

Surströmming... is a northern Swedish dish consisting of fermented Baltic herring. Surströmming is sold in cans, which often bulge during shipping and storage, due to the continued fermentation. When opened, the contents release a strong and sometimes overwhelming odor, which explains why the dish is often eaten outdoors...

[One] 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...

Because surströmming today contains higher levels of dioxins and PCBs than the permitted levels for fish in the EU, Sweden has had exceptions to these rules. The exception was 2002 to 2011, but an application for renewal of the exemption has been raised to the EU...

In April 2006, several major airlines (such as Air France and British Airways) banned the fish citing that the pressurised 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 airlines' decision "culturally illiterate," claiming that it is a "myth that the tinned fish can explode.

 Text from Wikipedia.   Photo: Swedish "klämma" with surströmming, potatoes and red onion on a "tunnbröd" with butter besides a glass of milk.