In Craster, on the Northumberland coast, a herring is split, gutted, brined, and hung inside a stone smokehouse that has stood for more than a hundred years, where it cures for sixteen hours over oak and whitewood shavings kept smoldering, never burning, until it comes out a kipper. It is raw the entire time, the way good sushi is raw, kept safe by salt and hours rather than heat. Four hundred miles east, on the Danish island of Bornholm, a herring goes onto a grill over a fire that is allowed to actually burn. It dries in the open flame for about two hours, the flames are smothered down to embers, and it smokes in the thick grey haze for two hours more, coming out fully cooked, the way a steak off a grill is cooked.

Cold smoking is the older trick and the harder sell to explain, because the smoke is doing less of the work than the name suggests. The temperature stays under about 85 degrees Fahrenheit, well below anything that cooks a protein, so nothing in the process actually kills bacteria the way heat does. The job falls entirely to salt: cold-smoked fish is traditionally cured in a heavy brine, historically run as high as fifteen or sixteen percent salt, long enough and strong enough to draw out moisture and make the flesh inhospitable to spoilage on its own. The smoke that follows adds flavor and a thin layer of its own antimicrobial help on the surface, but it is riding on a cure that would mostly work without it. A kipper is closer, chemically, to a cured ham than to a cooked fish.

Hot smoking flips every part of that arrangement. The temperature runs anywhere from about 120 up past 200 degrees Fahrenheit, hot enough that the fish has to reach 145 degrees at its center and hold there for half an hour, the same benchmark any oven or stovetop uses to call a piece of protein safely cooked. Because the heat itself is doing the killing, the salt in a hot-smoked fish is usually a token two or three percent, placed there for taste rather than preservation, and the whole process takes hours rather than the weeks a serious cold cure once needed. What comes out the other end flakes the way any cooked fish flakes, because it is one. On Bornholm, the tradition arrived with Scottish soldiers stationed at the old fort on Christiansø in the early 1800s, and the first proper smokehouse went up in the herring town of Gudhjem in 1866. Within a few decades the town had so many of them running at once that people started calling it the town of a hundred chimneys. The dish that made it famous, sol over Gudhjem, sun over Gudhjem, sets a whole hot-smoked herring topped with a raw egg yolk, radish, and spring onion: a fully cooked fish served under the one genuinely raw thing left on the plate.

So the two techniques are not two points on the same dial, one gentler than the other. They are a cure that happens to use smoke and a cooking method that happens to use smoke, sharing a word by accident of language rather than by any real kinship in the kitchen.

A tin flattens some of that difference back down, whether it means to or not. Canning a fish means sealing it and running the can through a retort, typically somewhere around 116 to 121 degrees Celsius, hot enough to sterilize whatever is inside regardless of what happened to it before the lid went on. A hot-smoked fish arrives at that step already cooked, so the retort just reseals and slightly extends a job the smokehouse had already finished. A cold-smoked fish arrives having never once been heated, cured but still raw, and the retort becomes the first real heat it has ever met, weeks after the smoke did. The cure that kept it safely raw for its first days on a shelf stops being the thing keeping it safe at all once a can takes over that job by force.

Which means a tin can never quite deliver the thing a cold smokehouse spends sixteen hours building. It can only deliver something cured like a kipper and then cooked like one anyway, because a shelf-stable can leaves the process no other option. The most faithful version of a cold smoke left anywhere might be the kind that was never built to survive a shelf at all: sold whole out of a stone building on a coast, eaten within the week, still raw when it reaches the plate.

The one edible part of the animal, and it isn't meat.

Sea urchin roe is not muscle, it is gonad, the only part of the animal worth opening a shell for. Paracentrotus lividus, the purple sea urchin named right on this tin, is common along the Galician and wider Mediterranean coast, where it has traditionally been eaten raw with a squeeze of lemon, long before Japan turned uni into a delicacy that can clear $360 a kilogram and draws in roughly fifty thousand tons of global demand a year.

Porto-Muiños packs this one in nothing but water and sea salt: no oil, no smoke, no sauce. What comes out is orange, smooth, and intensely of the sea, ready to eat straight from the tin with no cooking required.

Spread it cold on warm toast, or skip the toast and work it into a cream, a soup base, or a seafood sauce.

€24.00 for a 50g tin at Eat More Fish.