Surströmming (sour herring) is a national dish of Sweden that's basically just fermented herring. It's usually consumed in northern Sweden in August and September and used to be a common means of preserving surplus fish from a good catch. Said not to taste that bad as long as you don't breathe through your nose. Whether describing it as preserved when allowed to rot is technically accurate is debatable but the fact is that it's consumed by humans without inflicting lasting damage.
The only description of its preparation I can find is as follows:
- 35-40kg (80-90 lbs) stromming (herring)
- A large amount of coarse salt
- One 60 liter (16 gallon) barrel with ventilation valve
- One salinometer
Create a brine with a salinity of 23 degrees. One way to get the right brine concentration is to make holes in the
bottom of a bucket, fill it with the coarse grained salt, and filter the water through the salt.
Gut the fish and remove the heads.
Fill one third of the 60 l barrel with the 23 degree brine. Put in the fish, add salt on the top. Let it stand for a few hours. Then stir every third hour for the rest of the day.
The brine should be much less salty, about 11 degrees, because much of the dissolved salt will have been absorbed by the fish. Keep 5l of the brine, they call it the blood brine. Sieve the fish and throw away the remaining brine. Make another 20l of 12 degree brine. Fill the plastic barrel to one third with brine; these 20l should include the 5l blood brine, and add the fish. Put on the lid. Keep it at 17 to 18°C (63-65°F). You must use the ventilator to prevent it from exploding becasue of gaese released during the fermentation. It will be ready in mid August. It
Surströmming is not for the faint-hearted, Swedes included. One way of eating it is wrapped in thin slices of local bread (tünnbrod). Fillet the fish and roll it up in the bread along with raw onion and boiled potato. Potato of course is not part of the traditional recipe. A generous amount of vodka or aquavit is recommended, as an accompaniment if not for dutch courage before eating. Some people drink beer or milk with it.
If canned, opening the tin is usually done underwater since the fermentation causes a buildup of gases that results in a squirt of smelly stuff when the tin is punctured.
I haven't been there but I hear that the city of Örnsköldsvik has a museum dedicated to surströmming, opened in 2001 (the museum, that is, not the barrel of rotting fish). They've built it at a safe distance from the town. Stockholm, on the other hand, forbids opening tins of the stuff in apartment buildings since not all Swedes are fond of it and neighbours are likely to protest when the smell spreads through the hallways.