Soupe au Poisson

Soupe au poisson is a traditional soup of the Provencal Mediterranean coast, distinct from the more famous bouillabaisse though they share the same coastline. The soup is built on small bony rockfish — the species that have little commercial value individually but collectively give deep flavor — which are cooked with aromatics, then pressed through a fine sieve (a food mill or a conical chinois) so that the bones, skin, and solids are separated and only the extracted liquid and the fish's dissolved gelatin pass through. The result is a smooth, intensely flavored soup, thickened by the natural gelatin and emulsified with olive oil. Saffron and sometimes pastis give the Provencal perfume. The soup is served with croutons, grated Gruyere or Parmesan, and a spoonful of rouille.

A bowl of soupe au poisson is deep orange-red, smooth and velvety, with a powerful, complex flavor — the concentrated savor of the rockfish, the warmth of saffron, the fruit of the olive oil, sometimes a faint anise from the pastis. The texture is thick and coating from the dissolved gelatin; a handful of croutons, grated cheese, and a spoonful of rouille are stirred in at the table, turning the soup into a richer, more textured dish.

Soupe au poisson rests on the extraction of flavor and gelatin from bony rockfish and their emulsification with olive oil. Small whole fish — heads, bones, skin, and all — are simmered with white wine, tomatoes, garlic, fennel, and saffron; the long simmer dissolves the collagen from the bones and skin into gelatin, which thickens the liquid. The entire contents are then pressed through a sieve: the liquid passes through, carrying the dissolved gelatin and the extracted flavor compounds; the bones, skin, and other solids are left behind and discarded. Olive oil, beaten in at the end, emulsifies with the gelatin-rich liquid to give a smooth, velvety texture — the same principle as a mayonnaise, but with gelatin rather than egg yolk as the emulsifier.