How to Make Hákarl
Hákarl is Iceland's traditional fermented shark, made from the Greenland shark (Somniosus microcephalus). In its fresh state, the meat is neurotoxic due to extremely high concentrations of urea and trimethylamine oxide (TMAO). The fermentation process utilizes endogenous enzymes and microbial action to convert these compounds into ammonia, which is then allowed to dissipate during a lengthy drying phase. This transformation renders the flesh safe for human consumption, resulting in a product characterized by a potent ammonia aroma and a flavor profile often compared to very strong blue cheese.
Category: Fish & Seafood · Method: Alkaline · Time: 3-12mo · Difficulty: 3/5 · Yield: varies · Temp: 4-10°C
History
Greenland shark contains high levels of urea and trimethylamine oxide, making it poisonous fresh. Medieval Icelanders discovered that fermenting and drying the flesh made it safe to eat. It became a way to use every part of valuable catches. Today it's a cultural touchstone, especially during Þorrablót winter festival.
Ingredients
- Varies Greenland shark meat — Fresh shark, cut into large pieces
- - No other ingredients — Traditional method uses no salt or additives
Equipment
- Shallow pit or gravel bed
- Stones for pressing
- Drying shed with good airflow
- Hooks for hanging
- Patience
Instructions
Prepare shark
Cut fresh Greenland shark into large sections. Remove entrails and cartilage. WARNING: Fresh Greenland shark is neurotoxic and must never be consumed raw. The meat contains high levels of urea and TMAO which act as an antifreeze in the deep-sea shark but are poisonous to humans.
Time: Hours
Tip: Handle fresh shark carefully; use dedicated tools to avoid cross-contamination with other foods.
Fermentation (Traditional or Modern)
Traditional method: Bury shark pieces in a shallow pit of gravelly sand, pressing with heavy stones to squeeze out fluids. Modern method: Place shark pieces into perforated plastic containers (kassar). The weight of the stacked meat naturally presses out the fluids, which drain through the holes. This allows for better hygiene and easier monitoring than the burial method.
Time: 6-12 weeks
Tip: The goal is to allow the urea to convert to ammonia and drain away. The process is temperature-dependent: 6-8 weeks in summer, up to 12 weeks in winter.
Hang to dry
Once the meat is firm and the chemical conversion is complete, hang the strips in an open-air drying shed (hjallur). This stage is critical as it allows the ammonia to evaporate and the flavor to concentrate. Dry until a hard, brown crust forms while the interior remains pale and slightly soft.
Time: 4-5 months
Tip: Good airflow is more important than heat. The wind helps carry away the ammonia vapors.
Fermentation Timeline
- Day 1: Preparation — Shark cut and buried in gravel pit.
- Weeks 6-12: Fermentation — Underground fermentation. Toxins breaking down.
- Month 3: Digging up — Fermented shark retrieved. Strong ammonia smell.
- Months 3-8: Drying — Hanging in shed. Drying and further fermentation.
- Month 8+: Ready — Brown outside, pale inside. Ready to eat.
Signs of Success & Spoilage
Good signs
- Brown crusty exterior
- Pale, soft interior
- Strong ammonia smell (expected)
- Firm but yielding texture
- Cheesy/fishy taste
Warning signs
- Green color
- Slimy texture
- Truly rotten smell beyond ammonia
- Maggot infestation
Troubleshooting
- Uncertainty of safety
- Cause: Insufficient fermentation time or improper drainage Solution: If the fermentation duration was cut short or the meat did not drain properly, the batch must be discarded. Do not attempt to re-bury or 'restart' the fermentation once the drying phase has begun, as this introduces high risks of putrefaction.
- Too dry
- Cause: Over-exposure to wind or extended drying time Solution: Monitor the texture monthly. The exterior should be a tough rind, but the interior should retain a 'cheesy' consistency.
- Off-flavors (Non-ammonia)
- Cause: Bacterial contamination or poor drainage Solution: While hákarl smells of ammonia, any scent of standard rot, sweet decay, or visible mold (other than the brown rind) indicates failure. Discard immediately.
Storage
Refrigerated or in cool storage Keeps Months refrigerated. Store in well-sealed container to contain smell.
Health Benefits
- High protein
- Omega-3 fatty acids
- Traditional source of nutrients
- Low carbohydrate
- Historical survival food
- Cultural significance
Serving Suggestions
- Small cubes on toothpicks
- With Brennivín (caraway schnapps)
- During Þorrablót festival
- On rye bread
- As a traditional challenge
- With cold beer
Related Fish & Seafood Ferments
Other Alkaline Ferments
- Natto — Legumes & Soy
- Soybean oil cake — Legumes & Soy
- Century egg — Eggs
- Dawa-dawa (African locust) — Nuts & Seeds
- Ogiri (melon seed) — Nuts & Seeds