Boquerones en vinagre is the name of a Spanish dish that literally translates to "anchovies marinated in vinegar". It is simple to make and very popular when served as tapas, a kind of snack or appetizer. The dish involves marinating fresh, uncooked anchovies in vinegar — sometimes for several days — and then serving them with a dressing made of olive oil, garlic and parsley. Although the fish are not cooked with heat, the acidity of the vinegar causes a kind of chemical cooking that tightens the texture of the flesh and changes its color so it appears cooked. When boquerones en vinagre are eaten as tapas, the anchovies can be consumed by themselves, or they can be served on toasted pieces of bread or crackers.
The way in which the anchovies used in boquerones en vinagre are cleaned can dramatically affect the final presentation. For a more rustic appearance, the anchovies can have their heads removed, along with their innards and spine, leaving the skin and the tails on each. A more refined appearance can be achieved by actually filleting the small uncooked fish so the only part remaining is the inner flesh. They also can be gutted, have the head and tail removed, and then be cut down the middle to make two halves.
One important aspect about using raw anchovies, and many other raw fish, is the presence of a nematode known as anisakis, which can be harmful if eaten and potentially cause a severe allergic reaction. To kill the parasite, the fish must be frozen for a few hours; simple refrigeration will not kill it. It can be easiest to freeze the fish right after they have been cut and cleaned, although they also can be frozen after the dish is prepared.
The most common way to assemble boquerones en vinagre is to first place the cleaned, uncooked anchovies in a mixture of vinegar, salt and water. Some recipes call for the anchovies to be marinated for only a few hours, while traditional Spanish recipes leave them in the marinade for a few days. The two most often used types of vinegar in the dish are sherry vinegar and white wine vinegar.
Once the fish have finished marinating and have changed color so they have a paler, more cooked appearance, they are removed from the vinegar and placed in another dish. Olive oil is poured over them, sometimes just a little to coat and other times enough to submerge the fish. Chopped garlic and parsley are sprinkled over the oil, and the boquerones en vinagre are ready to be served.
Some presentations of boquerones en vinagre are very simple, just arranging the fish individually on a plate with oil over top. As tapas, they are frequently seen in a small boat-like container filled with a fair amount of olive oil. A more unique serving method has the fish rolled into a tight cylinder, almost like sushi, that is served standing on its side and drizzled in olive oil.