Hákarl: Iceland’s Fermented Greenland Shark (Complete Guide)

Let’s be honest about hákarl from the start: it’s not delicious in the conventional sense. Anthony Bourdain called it the single worst thing he’d ever eaten. Gordon Ramsay nearly vomited on camera. Every travel writer who visits Iceland includes a hákarl-tasting scene in their account, and the reaction is almost always the same — breathless, red-faced, reaching for the brennivín chaser that traditionally accompanies it.

And yet. The Icelanders kept making it for over a thousand years. Through famines and volcanic winters and centuries of geographic isolation, hákarl remained a food worth the extraordinary effort of its production. That persistence doesn’t happen by accident. Understanding hákarl properly means understanding not just the food itself, but the context in which a population develops a taste for extreme fermentation out of necessity — and then maintains that tradition long after the necessity has passed.

This is the most comprehensive guide to hákarl available in English: what it is, why Greenland shark needs to be fermented before it’s safe to eat, the precise chemistry of what happens during the 6-9 month curing process, how traditional Icelandic families make it, and how to taste it properly if you’re brave enough to try. You almost certainly cannot make hákarl at home in the traditional sense — but understanding it is an education in how far humans will go to create food from unpromising raw materials.

The Viking Problem: Why Greenland Shark Is Toxic

To understand hákarl, you first need to understand why Greenland shark (Somniosus microcephalus) needs extensive processing before humans can eat it. Fresh Greenland shark flesh is genuinely toxic — not metaphorically, not unpleasant, but pharmacologically dangerous. Eating it can cause symptoms resembling extreme drunkenness: vomiting, disorientation, muscle convulsions, and in large quantities, death. Dogs that eat Greenland shark behave as if severely intoxicated.

The toxicity has two primary sources. First, trimethylamine oxide (TMAO): Greenland shark, like other deep-sea sharks, uses TMAO as an osmolyte to survive the crushing pressures of deep cold water. When the shark dies, enzymes and bacteria convert TMAO to trimethylamine (TMA) — the compound also responsible for the smell of rotting fish — and dimethylamine. In large concentrations, trimethylamine causes the neurological symptoms described above.

Second, urea: Greenland shark has unusually high concentrations of urea in its flesh as another osmoregulatory adaptation. Fresh shark meat contains 2-3% urea by weight — enough to produce ammonia in significant quantities during digestion and when the flesh breaks down.

The fermentation and curing process of hákarl gradually eliminates both toxins. TMAO and TMA are volatile — over months of air-drying, they evaporate from the flesh. Urea is broken down by bacterial action and ammonia diffuses out of the flesh during the extended curing period. The resulting product still smells intensely of ammonia (the characteristic hákarl aroma) but at levels that are no longer toxic — the ammonia smell is the residue of the decontamination process, not active toxicity.

This represents one of the most remarkable examples of pre-scientific food safety knowledge in culinary history. Norse settlers in Iceland 1,000 years ago had no understanding of TMAO chemistry or urea metabolism. They simply observed that fresh Greenland shark made people sick, discovered through necessity and experimentation that burying it and drying it for many months made it safe, and transmitted that knowledge through generations. The process works because physics and chemistry are consistent regardless of whether you understand them.

Greenland Shark: The World’s Longest-Lived Vertebrate

A brief detour into the biology of the animal matters here, because it’s extraordinary. Greenland sharks grow slowly — perhaps 1cm per year — and can live to extraordinary ages. A 2016 study in Science by Julius Nielsen and colleagues, using radiocarbon dating of eye lens nuclei, estimated that the oldest female Greenland shark in their sample was approximately 392 years old, with an uncertainty range of ±120 years. This makes Greenland shark not just the world’s longest-lived vertebrate, but quite possibly the longest-lived animal with a spine — the shark you eat as hákarl may have been born before the Reformation.

Greenland sharks are harvested in Iceland, Greenland, Norway, and Canada, primarily as bycatch from cod and halibut fishing. Because they grow so slowly, they’re vulnerable to overharvesting; Icelandic hákarl production uses only sharks caught incidentally rather than from targeted shark fisheries, and production has declined significantly from historical levels. Traditional hákarl production is now a small-scale, regionally significant practice rather than a major industry.

The History of Hákarl in Iceland

The Norse settlers who arrived in Iceland in the 9th and 10th centuries found an island with limited agricultural potential and extraordinary marine resources. Greenland sharks were present in Icelandic waters and were large (up to 7 meters), easy to catch, and represented enormous quantities of protein. The problem was the toxicity — early settlers almost certainly learned through painful experience that fresh Greenland shark was dangerous.

The discovery of the curing process — burial followed by air-drying — likely happened incrementally. Sharks buried in gravel near the shore, originally to dispose of them or keep them cool, were discovered to have changed in ways that made them palatable after months. The gravel pits provided the slightly acidic, well-drained conditions that accelerated ammonia dispersal while keeping the flesh cool enough to prevent putrefaction of fats.

During the period of Icelandic history known as the “Dark Ages” (roughly 14th-18th centuries), when climate cooling reduced agricultural productivity and famines were frequent, hákarl’s importance as a protein source that could be prepared from an otherwise inedible animal was literally survival-critical. The cultural attachment to hákarl that persists today has roots in the food’s historical role as a famine food — something that kept people alive when other options were exhausted.

Contemporary Icelandic hákarl production is concentrated in the Westfjords region and on the Snæfellsnes peninsula, where traditional family operations still use methods largely unchanged since the Viking Age. The best-known producer is Björn Hjörleifsson of Bjarnarhöfn farm on Snæfellsnes, whose family has produced hákarl for six generations. His operation, which includes a small hákarl museum, is one of the primary destinations for food-curious tourists in Iceland.

The Production Process: How Hákarl Is Made

Traditional hákarl production follows a two-stage process spanning 6-9 months total. Modern commercial versions exist, but the traditional method is what we’ll focus on here.

Stage 1: Fermentation/Pressing (3-5 months)

The shark — typically caught in the winter months when they approach shallower waters — is gutted, beheaded, and cut into large pieces or left in large sections. The flesh is then buried in gravel pits or placed under heavy stones near the shore (historically) or in special draining boxes (in modern operations). The weight presses fluid from the flesh — the expelled liquid carries away toxins including urea and trimethylamine compounds.

The “fermentation” that occurs during this stage is not primarily lactic acid fermentation in the way that sauerkraut or kimchi ferments. The process is better described as controlled decomposition — enzymatic autolysis and microbial activity break down proteins and convert TMAO to volatile compounds that drain away or evaporate. The gravel or draining boxes allow continuous liquid removal while maintaining cool, slightly acidic conditions that keep the process moving in the right direction without complete putrefaction of the flesh.

Temperature matters enormously. Traditional hákarl is prepared in autumn-winter specifically because Iceland’s cool ambient temperatures (around 0-10°C during this period) slow microbial activity enough to prevent full putrefaction while still allowing the decontamination chemistry to proceed. In summer temperatures, the shark would rot before being safe to eat.

Stage 2: Air-Drying (4-6 months)

After the initial pressing period, the shark pieces are hung in traditional outdoor drying sheds — wooden-slatted structures that allow cold Icelandic air to circulate freely around the hanging flesh. The air-drying period is crucial for ammonia dispersal: the brown exterior crust that develops on hákarl is dried, oxidized flesh that also serves as the outer barrier through which ammonia slowly migrates outward from the interior.

During air-drying, the flesh transforms further: proteins continue denaturing and cross-linking; fats slowly oxidize (hákarl fat becomes amber-colored and slightly rancid in character, which traditional consumers distinguish as part of the authentic flavor); and the ammonia concentration gradually decreases from potentially toxic levels to merely intensely aromatic ones. By the end of air-drying, the exterior crust is brown-to-black and the interior is white to cream-colored — this interior portion is what’s eaten.

Stage 3: Cutting and Serving

The dried hákarl is cut into small cubes, the exterior crust removed, and served on toothpicks at room temperature. The traditional accompaniment is brennivín — Iceland’s signature aquavit, flavored with caraway and angelica, nicknamed “Black Death” by Icelanders themselves. The spirit’s anise-caraway character provides a herbal counterpoint to hákarl’s ammonia and provides the alcoholic mechanism for washing the smell from your palate between pieces.

What Hákarl Tastes Like — Honestly

The honest description: the smell hits you before you put it in your mouth. Ammonia, fish, and a chemical note reminiscent of very strong cleaning products or aged blue cheese at extreme intensity. Once it’s in your mouth, the ammonia sensation is persistent but not as sharp as the smell prepared you for — the flesh itself is chewy, slightly gelatinous, with a flavor that transitions from ammonia-forward to fishy to something almost nutty and complex in the finish. In the best hákarl from reputable producers, the finish is genuinely interesting.

The variation in quality is enormous. Mass-produced hákarl from tourist shops can be one-dimensional — just ammonia and old fish, with nothing else going on. Traditional farm-produced hákarl from proper producers like Bjarnarhöfn has a complexity that makes the ammoniac attack more bearable because there’s actually something worth tasting underneath it. Asking Icelanders about hákarl quality is like asking wine drinkers about plonk versus good wine — they’re aware that what tourists usually encounter is not the best version.

The brennivín pairing is functional, not merely traditional. The alcohol genuinely does clear ammonia from your olfactory receptors between pieces, allowing you to experience subsequent pieces more cleanly. If you’re going to try hákarl, bring brennivín. Or at least very strong aquavit or schnapps.

Can You Make Hákarl at Home?

In the traditional full sense — no, almost certainly not. Unless you live in Iceland or another Arctic country, you don’t have access to fresh Greenland shark, the cold climate needed for the pressing stage, or the traditional outdoor drying infrastructure. Even in Iceland, traditional hákarl is made by a handful of specialist producers, not home cooks.

What you can do is source imported hákarl. It’s available online through Icelandic specialty food importers (Norrona and Icelandic food suppliers ship internationally), at Scandinavian specialty stores in major cities, and sometimes at well-stocked Nordic or European food shops. Packaged hákarl comes vacuum-sealed in small cubes, ready to eat. The quality varies significantly; buying directly from a reputable Icelandic producer or importer is worth the effort.

There is a small-scale home curing tradition in Iceland for other fish (skate, herring) using similar principles of fermentation and drying, but hákarl specifically requires Greenland shark’s particular biochemistry to work as a culinary exercise rather than simply as a health hazard. Don’t attempt to ferment random shark species using this process — different shark species have different toxin profiles, and the hákarl method is calibrated specifically for Greenland shark.

The Nutritional Reality

Given the primary purpose of hákarl was survival nutrition, it’s worth noting what it provides. Greenland shark flesh — after curing — is high in protein (approximately 25-30g per 100g serving) and contains omega-3 fatty acids, B12, and selenium. The fermentation/curing process doesn’t significantly degrade the protein content. What it does produce is a very concentrated, shelf-stable protein source that keeps for months at room temperature — precisely what its original users needed.

In contemporary nutritional terms, hákarl is not a probiotic food in the same sense as lacto-fermented vegetables — the live bacterial cultures present during production don’t survive in meaningful concentrations in the finished dried product. Its health relevance today is more historical and anthropological than as a gut-health supplement.

Frequently Asked Questions

What is hákarl?

Hákarl (kæstur hákarl) is Iceland’s traditional fermented and air-dried Greenland shark. Fresh Greenland shark is toxic to humans due to high levels of trimethylamine oxide and urea; the 6-9 month curing process renders it safe by allowing these compounds to volatilize and drain away. The resulting product is intensely ammoniated in smell but nutritionally safe and traditionally significant in Icelandic culture.

Why does hákarl smell so bad?

The characteristic ammonia smell is the residue of the decontamination process. Urea in the shark flesh breaks down to ammonia during fermentation and curing; while most ammonia dissipates over the 6-9 months of production, the remainder creates the persistent aroma. This smell is paradoxically what confirms the shark has been properly processed — the ammonia you’re smelling is proof that the toxic compounds have been volatilizing away throughout the curing period.

Is hákarl safe to eat?

Yes — properly cured hákarl from reputable producers is safe to eat. The 6-9 month curing process reduces trimethylamine oxide and urea to non-toxic levels. However, home fermentation of Greenland shark (or other shark species) without expertise in the proper process is potentially dangerous. Only source hákarl from established Icelandic producers and distributors.

What does hákarl taste like?

Intense ammonia on the nose, then complex fish-and-ammonia flavor in the mouth, transitioning to something nuttier and more complex in the finish — particularly in high-quality examples. The texture is chewy and slightly gelatinous. The brennivín chaser (Icelandic schnapps) is strongly recommended to clear ammonia from your palate between pieces and make the experience more manageable.

Where can I buy hákarl?

In Iceland, hákarl is available at supermarkets (Krónan, Bónus), specialty food shops, and directly from producers like Bjarnarhöfn farm. Outside Iceland, look for Icelandic specialty food importers online, Scandinavian food shops in major cities, or Nordic specialty online retailers. Quality varies significantly — direct-from-producer or specialist importer versions are noticeably better than generic tourist-shop versions.

How do Icelanders actually eat hákarl?

Cut into small cubes (2-3cm), served at room temperature on toothpicks, alongside a shot of brennivín. Traditional consumption is at Þorrablót — the midwinter festival held in January-February that celebrates traditional Icelandic winter foods including hákarl, dried fish, lamb’s head (svið), and various other preserved foods. For most contemporary Icelanders, hákarl is a cultural touchstone eaten once or twice a year at Þorrablót rather than a regular food.

What’s the best way to try hákarl for the first time?

Outdoors if possible — the smell dissipates faster in open air. Have brennivín or strong aquavit ready as a palate cleanser. Take a small cube on a toothpick, breathe out before placing it in your mouth (reduces initial ammonia impact), chew thoroughly, and swallow before reaching for the brennivín. Give yourself a moment to process the finish before deciding whether you need to stop. Most people who try it once and find it awful would find a second piece, properly paced with the schnapps, more manageable.

One for the Record Books

Hákarl will never be a weeknight dinner. It’s an artifact of human ingenuity under constraint — proof that when the choice is between a toxic, otherwise unusable food source and starvation, people will figure out how to make the toxic source edible, and that the knowledge developed will persist in cultural memory for a thousand years even after the survival necessity has passed.

It represents something important about fermentation as a practice: the boundary between “food” and “not food” is not fixed. It’s determined by the accumulated processing knowledge of a culture. Fresh Greenland shark is not food. Hákarl is. The difference is a thousand years of trial, error, and expertise.

If you visit Iceland, try it. If you buy it from a reputable source, approach it the right way — outdoors, with brennivín, on a toothpick, with an open mind and a strong stomach. You’ll have a story worth telling, either way.