Fish velouté is the lightest of the three classical veloutés, built on fumet de poisson thickened with a white roux, and it serves as the base for the entire family of French fish sauces — from vin blanc to Normande to cardinal. The roux must be white: equal parts butter and flour cooked for 2-3 minutes over gentle heat, stirring constantly, until the raw flour smell dissipates but no colour develops. The fumet, warm but not boiling, is added in three stages — first a splash whisked in to form a paste, then a larger addition whisked smooth, then the remainder in a stream. This staged addition prevents lumps more effectively than adding all the liquid at once. The velouté simmers for 20-30 minutes, skimmed regularly as starch impurities rise to the surface. Unlike meat veloutés, which benefit from longer simmering, fish velouté must not cook beyond 30 minutes — the delicate fumet flavour degrades with extended heat. The finished velouté should be ivory-coloured, silky in texture, and taste clearly of fish with no trace of flour paste. If it tastes floury, the roux was undercooked or the simmering time was insufficient. Pass through a chinois for absolute smoothness. The velouté is rarely served as-is; it is an intermediate sauce that becomes suprême, vin blanc, or Normande through the addition of cream, egg liaison, or specific garnishes.
White roux only — no colour, 2-3 minutes cooking to eliminate raw flour taste. Add warm fumet in three stages to prevent lumps. Simmer 20-30 minutes, no longer — fish flavour degrades with extended heat. Skim regularly as starch impurities surface. An intermediate sauce — always finished before service.
For the silkiest texture, blend the finished velouté briefly with an immersion blender then pass through a chinois — this breaks any micro-lumps invisible to the eye but perceptible on the palate. If the velouté will become sauce vin blanc, reduce the fumet by one-third before making the roux — the concentrated flavour survives the cream and egg additions better. A splash of dry vermouth instead of white wine in the fumet gives a more complex aromatic base.
Overcooking beyond 30 minutes — the delicate fish flavour turns stale and flat. Using a blond or brown roux — wrong colour and flavour for fish sauce work. Adding cold fumet — temperature shock causes lumps. Using oily-fish fumet — the velouté will taste heavy and fishy rather than elegant.
Escoffier, Le Guide Culinaire; Larousse Gastronomique