Baccalà

Baccalà is cod, Gadus morhua, Atlantic cod, split open, boned and packed in dry salt. Salting draws water out of the flesh until bacteria cannot survive in it. It is a preservation technique, not a cooking method, and it predates refrigeration by five centuries.

The salted fish loses about forty per cent of its weight and turns stiff, pale and crusted with salt crystals. Before cooking it has to be desalted: soaked in cold water for one to two days with frequent changes. Only then does it regain its texture and become edible.

The distinction worth learning immediately is the one with stoccafisso. Same fish, two techniques: baccalà is salted, stoccafisso is air-dried in cold wind with no salt whatsoever. They soak differently, cost differently, taste differently and behave differently in the pan. Almost every confusion around Italian cod cookery traces back to this one point.

Concentrated cod: meatier, saltier and far more assertive than the fresh fish. Salting firms the proteins, so properly desalted baccalà flakes into wide, translucent, almost meaty leaves rather than falling apart into shreds. Fresh cod is delicate; baccalà is emphatic.

Underneath the salinity there is a clean sweetness and a mineral note that people who dislike 'fishy' fish tend to find surprisingly easy. It is not oily, so it does not taste of anchovy or mackerel; it tastes of the sea in a much cooler register.

Well desalted, it should taste of fish with only a whisper of salt. If it stings the tongue, it needs more water. If it tastes of nothing, someone soaked it for four days and washed the flavour out along with the salt.

Everything starts with the soak, and getting it wrong ruins the dish before you have cooked anything. Rinse the surface salt off under running water, then submerge the fish in plenty of cold water in the refrigerator for 24 to 48 hours depending on thickness, changing the water every eight hours. Keep the piece skin side up so the salt sinks away from the flesh rather than sitting under it.

Test before cooking. Pull a flake from the thickest part and taste it raw: it should taste of fish with only a hint of salt. Stinging on the tongue means more water; tasting of nothing means you have gone too far.

Then cook it gently. Baccalà hates a rolling boil: braise it covered on the lowest heat and move the pot rather than stirring with a fork, or the fish breaks up.

The classic Italian treatments are fried in light batter and eaten scalding, as in Rome; simmered briefly and dressed cold with oil, lemon, olives and parsley, as at a Neapolitan Christmas; and braised with tomato, garlic and parsley, as in Livorno. Salt goes in at the end, if at all, and usually not at all.

Dry salted cod in its original state is preserved by the salt itself and keeps for months in a cool, dark, airy place, ideally 10 to 15 C, loosely wrapped in paper or hung rather than sealed in plastic, since trapped moisture makes the surface tacky. The change to watch over time is in the fat: the flesh yellows from white to straw and the smell turns oilier as it oxidises, and it moves faster in warmth. Vacuum packs and pre-soaked pieces are a different case entirely and carry a date printed by the seller, which is the only reference for those.

Once it has been soaked out, it stops being a preserved product and behaves like fresh fish. Do the soaking in the fridge at 0 to 4 C with the water changed several times, then keep the drained pieces covered in the fridge and use them within a day or two. Soaked portions freeze at minus 18 C for a couple of months, though the flesh flakes more loosely on thawing and releases water into the pan.

Two dried fish sit side by side and only one is baccala. Salt cod is stiff but still bends, is coated in visible salt crystals, and shows thick ivory flesh with the grain running long; stockfish, stoccafisso, is unsalted, dried to the hardness of a plank and pale grey-brown, and it is the one Venetian baccala mantecato is actually made from. On the label, look for the species: Gadus morhua from Norway, Iceland or the Faroes is the reference cod, and Nordic or Norwegian origin usually comes with a thicker loin.

In shops abroad the word salt fish covers a wider net. Caribbean and West African grocers often sell salted pollock, saithe or ling, which come as thinner, narrower, more yellow-toned pieces and cost far less per kilo than cod. Ask for the loin, il filetto, the thick centre cut, rather than the tail and belly flaps that dry hard. A yellow cast across the flesh is oxidised fat rather than salt, and the difference in price between true cod and its substitutes is usually two to three times.

In the US, salt cod is widely available in Italian, Portuguese, Spanish, Caribbean and West African grocers, typically 12 to 20 dollars per pound for whole dried sides and rather more for boneless loin. Many Italian delis also sell it pre-soaked in the refrigerated case, which is convenient, but cook it the same day.

In the UK, Portuguese and Spanish delicatessens are the most reliable source, at roughly 18 to 30 pounds per kilo, with Brixton, Stockwell and the Portuguese quarters of most large cities the obvious places to look. Some fishmongers will salt cod to order given a few days' notice.

Buy on thickness, not on price per kilo: a piece three to four centimetres thick from the front of the fish stays in whole pieces through a long braise, while thin tail pieces shred (fine for fritters and croquettes, and half the price). Flesh should be white to pale ivory and firm; yellow or brown patches mean the fats have oxidised and no amount of soaking will fix the rancid taste. Remember that dry weight is not cooked weight: a kilo of dried salt cod becomes about a kilo and a half once rehydrated.

Vicenza and its province, where the dish is an institution. Sandrigo, just north of the city, holds a festival every September, and the version served there follows the recipe codified by the local confraternity, with polenta, as the rule requires. Be aware that what you will be eating is stockfish.

Venice, where the bacari of Cannaregio and San Polo serve baccalà mantecato on grilled polenta as a cicchetto: a couple of euro each, eaten standing at the bar, and one of the best ways to start an evening anywhere in Italy.

Rome, and specifically the tiny fried-cod counter at Largo dei Librari behind Campo de' Fiori, which has fried fillets and almost nothing else for decades. Naples, where salt cod is the fish of Christmas and the fishmongers of the Pignasecca market keep tubs of it soaking from the first days of December.

Livorno for the tomato version, and the Calabrian coast for a whole family of preparations almost unknown outside the region.