August is the "season" of sour herring.
Herring caught in the spring hits the market as surströmming at the end of August. Diehard surströmming eaters won't go for this year's catch, though; instead, they'll eat last year's surströmming, citing its maturation and tenderness.
Editor's note: Stinky Foods is a new weekly series that focuses on unusually pungent foods from around the world. Tune in next week for a new smelly delicacy.