Surströmming (pronounced [²sʉːˌʂʈrœmːɪŋ], Swedish for "sour herring") is fermented Baltic Sea herring that has been a part of traditional northern Swedish cuisine since at least the 16th century.
Just enough salt is used to prevent the raw fish from rotting (chemical decomposition). A fermentation process of at least six months gives the lightly-salted fish a characteristic strong smell and somewhat acidic taste.
When a can of surströmming is opened, the contents release a strong and sometimes overwhelming odor. The dish is ordinarily eaten outdoors. According to a Japanese study, a newly opened can of surströmming has one of the most putrid food smells in the world, even more so than similarly fermented fish dishes such as the Korean hongeohoe or Japanese kusaya.