Sandwich Rollmops

Unpin the skewer from a rollmops and the coil springs loose: a single herring fillet that has spent days slackening in vinegar, wound around a strip of gherkin and a few rings of raw onion. That coil is the sandwich before any bread is involved. The fish has already been filleted, brined, soured, and seasoned from the inside, so the build adds almost nothing: a firm split loaf, a thin layer of butter on the crumb, the herring laid in along its length or sliced into pinwheel rings, and the onion and gherkin from the coil spread back through. In the French Nord this lands on bread; everywhere else it is eaten straight off the fork.

The vinegar is the whole event. The herring is sour. The onion is sharp. The gherkin is sharper. Nothing in the coil is mild, and the sandwich does not try to add a single flavour to that stack. Its one job is to give all that acid somewhere soft to land.

Butter is the landing pad, and it is not optional the way it might be on a milder fish. Spread thin or skipped, and the vinegar hits the dry crumb directly and reads as a mouthful of pickle juice; spread properly, the fat coats the bread, rounds the brine's edge, and carries the salt across the bite the way it would under a salt-cured charcuterie. The bread has to be firm-crusted for a second reason: an open, soft loaf drinks the marinade off the fish within a minute and goes slack and grey, while a tight crust holds the brine at the surface and stays structural. Over-fill it and the onion rings slide out the back end on the first bite; under-fill it and the loaf tastes only of vinegar with no fish to answer it.

Open one and the smell arrives first and unmistakable, clean cold brine and raw onion with a metallic edge of vinegar behind it. The fish is soft and slightly translucent, pale grey going to silver at the skin, and it folds rather than flakes. The first bite is cool and bracingly sour, the herring giving way soft against the teeth, an onion ring snapping through with its own sharp burst, the gherkin loud and crisp beside it. The butter shows up a beat late, slick and quieting, pulling the acid back from the edge. There is nothing warm anywhere in it; the whole sandwich is cold from the jar.

The preparation is German before it is French, and its home grammar is a bar one. In old Berlin pubs the rollmops sat in tall glass cases on the counter called Hungerturm, hunger towers, alongside hard eggs and Mettwurst, sold by the piece to drinkers; the same fish is the centre of the Katerfrühstück, the hangover breakfast, where the salt and acid are reckoned to put a wrecked morning back together. France's northern coast, sharing the herring grounds and the curing habit, took it onto bread. You buy them from a jar by the piece, two or three to a portion, and ask whether they were rolled mild or sharp.

Variations move along the cure and what cushions it. A long-soured rollmops reads more bracing and wants more butter under it; a quick, mild one needs barely any; a smear of crème fraîche swapped for the butter rounds the whole thing toward the Northern open-face. What it is not is a Bismarckhering, the flat unrolled fillet from the same shelf, marinated whole rather than wound around a core, nor a fresh or smoked herring, both of which are not soured and ask the bread to do far more. The coil with its onion-and-gherkin core is the fixed point; only the sharpness and the cushion change. Its grouping here, with the French fish sandwiches, is Baguette Poisson.

A Berlin Bar Fish

The rollmops is a nineteenth-century German invention, and the conditions that made it were industrial rather than culinary. It took shape in the Biedermeier decades, the years after 1815, as the long-range railway pushed inland from the North Sea and Baltic coasts and carried barrelled herring to cities that had never had fresh sea fish. Pickling in spiced vinegar was the preservation that survived the journey, and Berlin made the rolled, skewered form its particular specialty.

The name is plainer than the dish. It joins rollen, to roll, with Mops, the word for a pug, the squat rolled shape reading as the dog; an alternative folk reading derives it from the English "roll-'em-ups", which is the kind of after-the-fact etymology that travels faster than it is proven.

Its cousin is better dated than the rollmops itself. The Bismarckhering is traditionally tied to the Stralsund fish merchant Johann Wiechmann, who is said to have sent a barrel of his marinated herring to Otto von Bismarck in 1871 and been granted leave to use the name; the confirming papers were lost when the town archive burned in 1944, so the story rests on trade memory rather than a surviving document.