You'll probably hear that the traditional way of fermenting shark or Hakarl is to bury it in the ground and then urinate on it before letting it rot for some months. This is not entirely true.
The urinating bit is true, but the shark doesn't rot, it ferments. And urine is no longer used in this process, but it was used back in the day before modern culinary techniques could be used.
The shark / Hakarl does actually smell of ammonia, which is where the urban myth comes from. It has been cured with a particular fermentation process, consisting of burying the shark underground and hanging it to dry for four to five months. This is done to get rid of the acid in the flesh which makes it impossible to eat fresh.
So the shark is not rotten (which some people wrongly believe) but it is fermented. There's a bit of a difference.
The result is, uhm, an acquired taste. Connoisseurs of very strong cheese may take a liking to it on the first bite. For others, well, let's just say it's not a common dish anymore; it is mostly the older generation in Iceland who still eat and enjoy it.
For a small fee, you can taste a sample in the food section of the Kolaportid flea market on the weekends. They just love selling samples to tourists to watch their faces turn sour! For the ones that are extra hardcore, rinse it down with a shot of Brennivín.
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Article from guidetoiceland.is