How to Make Surströmming
Surströmming is Swedish fermented Baltic herring, famous for being one of the world's most pungent foods. The process relies on the salt-tolerant bacteria *Haloanaerobium*, which thrive in the brine to produce carbon dioxide, hydrogen sulfide, and various organic acids. This specific microbial activity creates the characteristic pressurized cans and the intense, sulfurous aroma that defines this traditional northern Swedish delicacy.
Category: Fish & Seafood · Method: Lactic Acid · Time: 3-6mo · Difficulty: 3/5 · Yield: varies · Temp: 15-20°C
History
Surströmming emerged in northern Sweden during the 16th century when salt was expensive. Using less salt meant herring fermented rather than just preserved. The result became a regional tradition, with annual premieres in late August. It's survived as cultural heritage despite - or because of - its notorious reputation.
Ingredients
- 20 lbs (9kg) Fresh Baltic herring — Must be caught in spring (April-May) before spawning for optimal fat content.
- Approx. 3-4kg Sea salt (Non-iodized) — Used to create a 24% saturated initial brine and a 10-12% fermentation brine.
- As needed Water — Use filtered, chlorine-free water for brine stability.
Equipment
- Large barrels or tubs
- Canning supplies for final packaging
- Cold storage
- Outdoor opening space (essential!)
Instructions
Initial Pre-Brining
Place cleaned fish in a saturated salt brine (approx. 24% salinity) for 24 hours. This draws out blood and moisture, firming the flesh and inhibiting surface spoilage bacteria.
Time: 24 hours
Tip: The brine must be kept cold (approx. 4°C) during this phase.
Primary Fermentation
Transfer fish to barrels with a weaker brine maintained at 10-12% salinity. This concentration is critical: high enough to prevent Clostridium botulinum, but low enough to allow Haloanaerobium to thrive.
Time: 3-4 weeks
Tip: Maintain a temperature of 15-18°C. This is the only stage where warmth is used.
Canning and Cold Ripening
Seal the fish and brine into cans. Move immediately to cold storage (4-8°C). The fermentation continues slowly in the cans, producing gas that causes the lids to bulge.
Time: 3-6 months
Tip: Cold storage is mandatory to prevent the fish from turning into a slurry and to control gas pressure.
Fermentation Timeline
- May: Catch and prep — Herring caught. Initial preparation and brining.
- May-June: Barrel fermentation — Fish fermenting in barrels. Sour smell developing.
- June-July: Canning — Fish transferred to cans. Fermentation continues.
- August: Premiere — Third Thursday of August. Cans ready for sale and eating.
Signs of Success & Spoilage
Good signs
- Bulging cans (indicates active Haloanaerobium)
- Fish flesh is pinkish-gray and firm enough to hold shape
- Strong sulfurous/pungent aroma (like rotten eggs/vinegar)
- Brine pH between 5.0 and 5.5
- Clear or slightly cloudy brine
Warning signs
- Black mold or fuzzy growth on the fish or brine surface
- Putrid, 'death-like' smell that differs from the sharp sulfurous fermented scent
- Completely liquefied fish (indicates temperature was too high)
- Flat cans after 3 months (indicates fermentation failure)
- pH above 6.0 (safety risk)
Troubleshooting
- Cans bulging excessively/leaking
- Cause: Storage temperature too high Solution: Immediately move to a colder environment (0-4°C) to slow microbial activity.
- Fish is mushy or disintegrating
- Cause: Insufficient salt or high temp during primary fermentation Solution: Ensure brine is strictly 10-12% salinity and temperature does not exceed 18°C.
- Safety Concern: Botulism risk
- Cause: Salinity dropped below 10% Solution: Always use a salinometer to verify brine strength; never reduce salt below 10% for low-acid fish.
Storage
Keep cans cold; store opened fish in brine refrigerated Keeps 1+ year in can. ALWAYS open outdoors or underwater. Never open indoors.
Health Benefits
- High protein
- Omega-3 fatty acids
- Vitamin D
- Calcium (from bones)
- B vitamins
- Traditional food heritage
Serving Suggestions
- On tunnbröd (thin bread)
- With boiled potatoes
- With red onion and sour cream
- With dill
- Traditionally with milk or beer
- Always outdoors!
Related Fish & Seafood Ferments
Other Lactic Acid Ferments
- Sauerkraut — Vegetable
- Kimchi — Vegetable
- Kefir — Dairy
- Pickles — Vegetable
- Yogurt — Dairy
- Hot Sauce — Condiment
- Water Kefir — Beverage
- Kraut-Chi — Vegetable