Rouille

Rouille is the rust-coloured saffron and garlic emulsion served with bouillabaisse — a Provençal condiment so essential to the experience of Marseille's great fish stew that the soup cannot be said to exist without it. The name means 'rust' in French, which describes the colour accurately: a deep orange-red from saffron and piment d'Espelette or cayenne. Traditionally, rouille is made in a mortar: saffron is steeped in a spoonful of the bouillabaisse broth, then combined with garlic that has been pounded with salt, moistened bread or potato for body, and oil whisked in drop by drop until a thick emulsion forms. The result is essentially an aioli — a garlic and oil emulsion — with the addition of saffron, chilli, and a starch base that makes it thicker and more stable than aioli alone. The serving ritual is specific: rouille is spread generously on slices of grilled crouton (croûton frotté à l'ail), which are then floated on the broth. The rouille begins to dissolve into the soup as you eat it, seasoning each spoonful with saffron, garlic, and the richness of the emulsion. Some guests stir additional rouille directly into the broth at the table. Rouille should be thick enough to mound on a crouton without running off. Its heat should be warm rather than fierce. Its saffron colour should be vivid and its garlic presence unmistakable but not raw-tasting — the bread or potato moderates the garlic sharpness.