Deep poaching submerges a whole fish or large cut entirely in court-bouillon — a flavoured liquid of water, white wine, aromatics, and acid — cooking it gently at 70-80°C (never a rolling boil). The technique is fundamental to the poissonnier's repertoire and underpins dozens of classical preparations. The fish is started in cold court-bouillon for whole round fish (to ensure even penetration) or lowered into hot liquid for pre-portioned cuts and flatfish. The ratio is typically 1 litre of court-bouillon per 500g of fish, with the liquid composed of roughly 60% water, 25% dry white wine, 15% aromatics (onion, carrot, celery, bouquet garni, peppercorns, and a splash of white wine vinegar). The critical principle is frémir — the liquid should barely tremble, with lazy bubbles breaking the surface every few seconds. At 80°C, fish proteins denature gently: myosin sets between 40-50°C, providing structure, while collagen begins converting to gelatin around 60°C, yielding succulence. A 1.5kg whole sea bass requires approximately 20-25 minutes from cold start to reaching 62°C at the thickest point. The fish is done when a skewer inserted at the backbone meets no resistance and the flesh along the lateral line has turned opaque. Classically, the fish is lifted on a fish kettle rack (poissonière), drained briefly, and presented on a folded napkin with the skin removed tableside. The court-bouillon itself becomes the base for the accompanying sauce — reduced, strained, and mounted with butter or enriched into a velouté.
Frémir, not boil — maintain 70-80°C throughout Cold start for whole fish, hot start for portions Court-bouillon ratio: 60% water, 25% wine, 15% aromatics Use a poissonière (fish kettle) with removable rack Test doneness at the backbone with a skewer or probe thermometer to 62°C
For an ultra-clear court-bouillon, simmer the aromatics for 20 minutes and strain before adding the fish — this prevents vegetable fragments from marring the presentation Wrap delicate fish in muslin before poaching to maintain shape during cooking and lifting A splash of milk in the court-bouillon helps keep the flesh brilliantly white — the casein proteins bind tannins and impurities
Boiling the liquid, which causes the flesh to break apart and turn chalky Using too little liquid, leaving the fish partially exposed and unevenly cooked Starting a whole fish in hot liquid, causing the exterior to seize before the centre cooks Overcooking — fish continues to carry-over cook 2-3°C after removal Discarding the poaching liquid instead of using it as the sauce base
Escoffier, Le Guide Culinaire; Larousse Gastronomique