What is surströmming?
Surströmming. That's Swedish for "sour herring" and is fermented herring. They are plucked out of the Baltic Sea before they are stored for months to stew in their own bacteria through a carefully calibrated autolysis method which creates rather smelly acids, using just enough salt to prevent it from rotting. Don't look scared, this is an old food preservation method and has been around for thousands of years around the world.
When do you eat it?
The traditional 'surströmming premiere' is held on the third Thursday in August. That's when Swedes crack open their cans of surströmming – if the can has a slight bulge, don't worry, it's because the fermentation process continues even after the herring is canned.
How do you eat it?
Not like BuzzFeed's American staff, who published a video of themselves trying it for the first time, using words like "dead body" and "baby diaper" to describe the smell. They incensed one Swedish surströmming expert so much that he published his own instruction video to how to really enjoy this unusual delicacy.
Eat it with onion, sour cream, bread, potatoes and a glass of snaps.
But before you eat it, remember to store it correctly. Ruben Madsen of the Surströmming Academy on the island of Ulvön says "it must always be stored in a cool environment. If it is stored in a warm place, then the lactic acid destroys the proteins and there is no fish left inside the can".
It does have a strong smell, there's no denying that. If you don't like it, there are various tactics to mitigate it as much as possible. One is to open the can under water. Another is to eat it outdoors. Alternatively, as soon as you open the can, stick your nose as close as possible and take a deep breath to immunize yourself – nothing will smell bad after that.
Don't worry, it tastes better than it smells, after your nostrils get over that initial shock.
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And all Swedes eat this?
Admittedly, it is not to everyone's liking. Traditionally, it is also more common in northern Sweden, and especially on the north-eastern coastline around the High Coast and further north in the Norrland region.
Cans of surströmming. Photo: Ulf Palm/TT