A roux is equal parts fat and flour cooked together — the classical thickening agent for the entire béchamel, velouté, and espagnole sauce families. The ratio and method are fixed; only the colour and cooking time change depending on the intended application. White roux thickens without adding colour. Blonde roux adds a mild, nutty note. Brown roux adds depth and a distinctive flavour at the cost of some thickening power (the Maillard reaction partially denatures the starches that provide thickening).
- **Equal weight of fat to flour.** Not volume — weight. Flour is heavier than fat per volume. - **Cook long enough.** A white roux needs 2 minutes minimum to cook out the raw flour taste — the single most common failure in béchamel production. Blonde needs 4 minutes. Brown needs 8–10 minutes, watching constantly. - **Temperature matching.** Hot roux + hot liquid = lumps. Cold roux + cold liquid = lumps. Hot roux + cold liquid = smooth. Cold roux + hot liquid = smooth. Choose one or the other. - **Colour progression:** White (pale, raw dough smell): 2 minutes. Blonde (pale sand, faint nuttiness): 4 minutes. Brown (milk chocolate, roasted nuttiness): 8–10 minutes. Decisive moment: The colour and smell of the brown roux — when it smells distinctly of toasted nuts and the colour has reached dark caramel. This is immediately adjacent to burned (acrid, bitter). Watch without distraction from this point.
Jacques Pépin's Complete Techniques