Inlagd Sill: Swedish Pickled Herring in Vinegar

There is a jar in my fridge door that has been there, in one incarnation or another, since roughly October. It gets emptied and refilled. Around Christmas it earns its keep three times a week. The contents are herring, red onion and a sweet-sour brine built on a ratio so famous in Sweden that people recite it like a phone number: 1-2-3. One part vinegar, two parts sugar, three parts water.

The trouble is that the ratio was written for a bottle you probably cannot buy.

The herring that built the Baltic

Before it was a delicacy, herring was money. For roughly two centuries the Skåne Market at Falsterbo and Skanör — held every autumn from around the 1200s — was one of the largest commercial events in northern Europe, and its currency was salted Baltic herring. The Hanseatic League controlled the trade largely by controlling the salt: Lüneburg’s inland brine springs supplied the preserving agent, Hanse merchants supplied the barrels, and the herring came out of the Øresund in numbers that contemporary chroniclers described with the sort of exaggeration you reach for when the truth is already absurd.

Then the shoals moved. Herring in the North Sea and Skagerrak arrive in what Swedes call sillperioder — herring periods, decades-long booms when the fish crowd into the Bohuslän fjords in quantities that reshape the local economy, followed by decades when they simply do not come. Historians count several: roughly 1556–1589, 1660–1680, 1747–1809, and 1877–1906. During the great period of the late 1700s the Bohuslän coast filled with trankokerier, blubber-boiling works that rendered herring into lamp oil, and the fjords stank so badly that the effluent was blamed for killing the very fish it was made from. When the herring left in 1809, the region collapsed.

What survived was the salting habit. A barrel of herring under coarse salt keeps for a year; it also becomes nearly inedible, hard and savagely saline. Every Swedish herring preparation you now eat is a downstream solution to that problem — a way of taking a preserved protein and making it a pleasure again. Inlagd sill is the plainest and cleverest of those solutions: soak the salt back out, then reintroduce flavour on your own terms in an acid-sugar bath.

It is worth being precise about what this dish is and is not related to. Matjessill is a different animal — herring cured young in a sugar-salt-spice mix, the technique borrowed from the Dutch maatjesharing (“maiden herring”, caught before spawning, cured with the pancreas left in so its enzymes ripen the flesh). Surströmming is fermented in the tin and belongs to another conversation entirely. Inlagd sill is the everyday one, the one on the julbord, the one at Midsummer next to the new potatoes and the aquavit that also chase gravlax.

Watering out: the step everyone rushes

Buy salt herring — saltsill or saltad sill — in fillets, from a Nordic delicatessen or online. It arrives packed in dry salt or a heavy brine, and it is genuinely inedible as it stands. The Swedish term for what happens next is urvattning, watering out, and it is diffusion doing the work: salt migrates from the high concentration inside the fish to the low concentration in the bowl, until the two roughly equalise.

Twelve hours in cold water, three changes, in the fridge. Each change resets the gradient and speeds the process; leaving the fillets in a single bowl of increasingly salty water stalls it.

Do not overshoot. Once the fillets are properly watered, more soaking removes nothing useful and starts pulling out the salt that holds the muscle proteins in a firm gel. Over-watered herring goes soft and slightly cottony, and there is no way back — you cannot re-firm it in the brine, because the brine has no salt to speak of. Taste a corner of a fillet at the 12-hour mark. It should read as seasoned fish, the way a good anchovy fillet reads as seasoned rather than as salt.

If your kitchen runs warm, keep the bowl in the coldest part of the fridge. Watering out at room temperature gives spoilage bacteria a low-salt, high-moisture protein at exactly the temperature they enjoy most.

Which herring, and why size matters

The fish is Clupea harengus, Atlantic herring, and the ones that end up in a salt barrel are usually caught in the Skagerrak, the Kattegat or the Baltic. Baltic herring — strömming — is a smaller, leaner subspecies adapted to brackish water; south of a line drawn roughly at Kalmar the same fish is legally called sill, and north of it strömming, which is one of the more charming pieces of Swedish food bureaucracy. For inlagd sill you want the fatter Atlantic fish. Lean strömming fillets take the brine too fast, go sharp, and lack the fat that carries the allspice.

Fat content is the whole argument for making this in autumn and eating it in winter. Herring caught after the summer feeding season can carry 15–20% fat by weight; the same fish in spring, spent from spawning, drops to 2%. Autumn-salted fish is why a December jar tastes richer than a June one, and it is why the Swedish calendar puts the biggest herring table at Christmas rather than Midsummer, even though Midsummer gets the songs.

The 1-2-3 problem, and the arithmetic that fixes it

Swedish recipes say one part ättika, two parts sugar, three parts water. Ättika is 12% acetic acid. It is sold in every Swedish supermarket and almost nowhere else. Distilled white vinegar in the UK is typically 5–6%.

Follow 1-2-3 with 6% vinegar and you get a brine at 1% acidity. The original ratio works because one part of 12% acid in six total parts gives a final brine of roughly 2% acetic acid, and that number is doing real work. Below about 1.5% the brine tastes flabby and the keeping quality drops sharply; around 2% you get the clean, nose-tingling sourness that makes the sugar bearable.

So scale the vinegar up and the water down, keeping the sugar constant relative to the whole:

• Swedish original: 100 ml ättika (12%) + 200 g sugar + 300 ml water → 2% acid
• What you make: 200 ml white vinegar (6%) + 200 g sugar + 200 ml water → 2% acid

Same acidity, same sweetness, same volume. If you find 5% vinegar, use 240 ml vinegar and 160 ml water. If you somehow have ättika, use the original numbers.

The other rule is temperature, and it is absolute. The brine goes on cold. Herring flesh denatures at low temperatures — well under 50°C — and warm brine will turn the translucent, faintly resilient fillet into something opaque and mealy in minutes. Warm the brine only enough to dissolve the sugar, then chill it properly. I put the pan in a sink of cold water for twenty minutes, then the fridge for two hours, and I check with a thermometer, because “cool to the touch” is a phrase that has cost me a jar.

The small clever twist

Toast the allspice and white peppercorns before they go in.

Ninety seconds in a dry pan, shaking, until the allspice smells like clove and pine and warm resin rather than like a spice drawer. The volatile oils in Pimenta dioica — eugenol chiefly, the same compound that makes cloves clove — are far more available after the berry has been heated, and the cold brine has three weeks to pull them out. The difference is not subtle. Untoasted allspice gives you a background note; toasted allspice makes the brine taste as though it has been aged twice as long. Tip the spices onto a cold plate the second they smell right; carryover heat in a hot pan will take them to bitter.

Building the jar

Cut the watered fillets crossways into 2 cm pieces, skin on. The skin is thin, silvery and pleasant, and it holds the piece together.

Layer everything into a sterilised 1-litre jar: herring, then onion rings, then a scatter of carrot and spice, and repeat. Pack it snugly enough that the pieces support each other and nothing floats above the brine line. Anything sitting proud of the liquid will oxidise and go grey-brown within a couple of days.

Pour over the cold brine, seal, and wait 48 hours. The first day it tastes of vinegar; the second, the sugar and the fish have met in the middle. At four days it is properly good. At a fortnight it is better than at four days, which is the argument for making a big jar in November and letting it coast into December.

Where it goes wrong

Mushy herring. Either you overwatered, or the brine was warm. Both are unrecoverable.

Tastes only of vinegar. Your vinegar was stronger than you thought, or you used cider vinegar, which brings its own fruit acid and a muddier flavour. Stick to plain distilled white.

Cloudy brine after a week. Usually onion. Red onion sheds anthocyanins and a little starch; a faint rose-tinted haze is normal and harmless. A thick, ropy cloudiness with a yeasty smell means the acidity was too low — check your arithmetic and start again.

Bitter after a month. Bay leaves left in too long. If you are keeping a jar beyond three weeks, fish them out at day 10.

Variations, and where it sits at the table

Senapssill — mustard herring. Drain 300 g of the finished inlagd sill and fold it into a sauce of 3 tbsp Swedish sweet mustard, 1 tbsp Dijon, 2 tbsp white wine vinegar, 1 tsp sugar, 100 ml rapeseed oil whisked in slowly, and a fistful of dill. It sits alongside the mustard-and-dill sauce that goes with cured salmon as one of the two great Swedish mustard sauces.

Löksill — double the onion, halve the carrot, add a sliced leek. Blunter and better on rye.

Glasmästarsill — glazier’s herring — keeps the fillets in longer pieces and adds horseradish and ginger. Same brine, more heat.

Serve it cold, straight from the jar, with waxy new potatoes, a spoon of soured cream, chives, and a plank of rye crispbread made from scratch. A very cold aquavit is traditional and, at Christmas, close to compulsory. On the julbord it goes first, before the meatballs and cream sauce and long before anyone opens the sprat and cream potato gratin — herring first, then everything else, then more herring while you pretend to consider dessert.

Three weeks in the fridge, and the jar earns its place in the door.