On Surstromming

"The way surströmming is made explains why it smells so bad. Fish caught in the spring off the Gulf of Bothnia coast are packed into a barrel with salty brine that prevents them from rotting entirely. The fish ferment in the barrel for a month or so, aging in a stew of lactic acid bacteria and enzymes.
Surströmming is then sealed in big round cans, with pressure building up so aggressively inside that they bulge at both ends—and sometimes burst."

Sweden Has Champagne Aspirations for Its Smelly Fermented Herring
by Sven Grundberg
http://online.wsj.com/article/SB10000872396390444914904577617300957144354.html