Hákarl is fermented Greenland shark, a traditional Icelandic food famous for its intense ammonia smell and acquired taste. The shark meat is toxic when fresh, so Icelanders developed a fermentation and drying process over centuries to make it safe to eat. Today it remains a cultural staple in Iceland, particularly during the midwinter festival of Þorrablót, and a notorious challenge for adventurous tourists.
Why the Meat Starts Out Toxic
Greenland sharks lack a urinary tract, so waste compounds build up directly in their flesh. The main culprit is trimethylamine oxide, or TMAO, a chemical the shark accumulates in high concentrations throughout its body. When eaten fresh, bacteria in the human gut convert TMAO into trimethylamine, which causes symptoms resembling severe intoxication: confusion, nausea, stumbling, and in extreme cases, convulsions. Early Icelandic settlers reportedly learned this the hard way, then figured out that processing the meat could neutralize the toxin.
The Greenland shark itself is a massive, slow-moving deep-sea predator found in the cold waters of the North Atlantic and Arctic. It can grow over 20 feet long and live for several centuries, making it one of the longest-lived vertebrates on Earth. Icelanders historically called it “hákarl,” Greenlanders call it “ekalugssuak,” and Norwegians know it as “hakjerring.”
How Hákarl Is Made
The production process has two distinct phases: fermentation and drying. Traditionally, shark meat was buried in gravel pits and weighted down with stones, allowing it to ferment under pressure. Modern producers use plastic containers with drainage holes, but the chemistry is the same.
During the fermentation phase, which lasts roughly seven to eight weeks, microbial activity transforms the meat. TMAO levels drop below detectable levels within the first five weeks as bacteria break it down into trimethylamine and dimethylamine. These breakdown products are what give hákarl its signature ammonia punch, but they’re far less dangerous than the original compound. The pH of the meat rises from around 6 (slightly acidic) to about 9 (strongly alkaline), creating an environment that shifts which bacteria dominate. In the early weeks, salt-tolerant marine bacteria do most of the work. By the final fermentation phase, different bacterial communities take over and drive the production of the pungent amine compounds.
After fermentation, the meat is cut into strips and hung in a drying shed (called a “hjallur”) with open sides that allow wind to pass through. This drying phase lasts about five weeks. Bacterial counts that spiked during fermentation decline as moisture leaves the meat. Producers traditionally judge readiness by the smell and by the formation of a dry, brown crust on the outside while the interior remains soft.
Two Types of Hákarl
The finished product comes in two varieties depending on which part of the shark it comes from. Glerhákarl, meaning “glassy hákarl,” is cut from the meat closest to the skin. It has a chewier, more reddish appearance. Skyrhákarl comes from the shark’s inner flesh and has a softer, whiter texture that some compare to a strong, pungent cheese. Both types carry the same ammonia-heavy aroma, but skyrhákarl is generally considered milder and more approachable for first-timers.
What It Tastes and Smells Like
The smell hits you first. Most people describe it as overwhelming ammonia, similar to very strong cleaning products. The taste is milder than the smell suggests, though still intensely fishy and sharp. The texture varies by type but tends to be firm and slightly rubbery for glerhákarl, softer and creamier for skyrhákarl. First-time tasters often find the ammonia flavor lingers in the mouth and sinuses well after swallowing.
Hákarl is traditionally served in small cubes, often on toothpicks. The classic pairing is with brennivín, an Icelandic caraway-flavored spirit sometimes nicknamed “the Black Death.” A shot of brennivín serves a practical purpose: it helps cut through the strong aftertaste. In Iceland, this combination of fermented shark and a shot of brennivín is a well-known ritual, especially at festivals and cultural gatherings.
Cultural Significance in Iceland
Hákarl’s origins are rooted in survival. Iceland’s harsh climate and limited arable land meant that early settlers could not afford to waste any potential food source, even one that was poisonous in its raw state. The fermentation technique likely developed through trial and error as a way to preserve protein through long winters. Over time, it became more than sustenance. It became a point of national identity.
The dish is most prominently featured during Þorrablót, a midwinter festival where Icelanders eat a spread of traditional preserved foods including dried fish, smoked lamb, and hákarl. For many Icelanders, eating hákarl at Þorrablót is a way of connecting to their heritage rather than an everyday meal. Outside the festival, you can find it year-round in Reykjavik’s specialty shops and at the Bjarnarhöfn Shark Museum on the Snæfellsnes peninsula, which has produced hákarl for generations.
Conservation Concerns
The Greenland shark is currently classified as Vulnerable on the IUCN Red List, with a decreasing population trend. It was upgraded from Near Threatened in 2006 to Vulnerable in 2020. The species reproduces extremely slowly, consistent with its extraordinary lifespan. Most hákarl produced today comes from sharks caught as bycatch in fishing nets rather than from targeted hunting, but the species’ declining numbers and slow reproduction rate make any harvesting pressure a concern. Iceland does not have a large-scale commercial hákarl industry, and production remains relatively small and artisanal.