Liaison in French cooking refers to any mixture used to thicken, enrich, and bind a sauce, soup, or stew, transforming a thin liquid into a smooth, velvety, clinging preparation. The classical repertoire includes five principal liaisons, each producing a different texture, flavour, and finish: roux (flour and fat), egg yolks and cream, beurre manié, starch slurry, and blood. Understanding which liaison to use and when is one of the most important skills of the saucier and tournant. The roux (equal parts flour and fat, cooked together) is the most common liaison, forming the base of béchamel, velouté, and espagnole. White roux (cooked 2-3 minutes, no colour) thickens white sauces; blonde roux (4-5 minutes, pale gold) thickens veloutés; brown roux (8-10 minutes, deep brown) thickens espagnole and brown sauces, though its thickening power diminishes as it darkens. The egg yolk and cream liaison (liaison finale) is the most luxurious — egg yolks beaten with cream, tempered with hot liquid, and stirred back into the sauce. It produces a silky, custard-like finish used in blanquettes, veloutés, and cream soups. The critical rule: never boil after adding — above 82°C the yolks coagulate and curdle. Beurre manié (equal parts soft butter and flour, kneaded together) is the emergency thickener — whisked into a simmering liquid in small pieces, it disperses the flour evenly without creating lumps. Used to rescue a too-thin sauce without starting over. Starch slurry (cornflour or arrowroot mixed with cold water) produces a clear, glossy thickening without the opacity of roux — preferred for transparent sauces and fruit coulis. Blood liaison (sang) is the most dramatic — animal blood mixed with vinegar or cream, stirred into a reduced sauce off the heat. Used in civet de lièvre and traditional coq au vin. It produces a dark, opaque, velvet sauce of extraordinary body. Each liaison has its place, and the choice defines the finished dish's character as surely as the principal ingredient.
Five classical liaisons: roux, egg yolk/cream, beurre manié, starch slurry, blood. Roux: white (no colour), blonde (pale gold), brown (deep) — thickening power decreases as colour deepens. Egg yolk/cream: temper first, never boil after adding (82°C max). Beurre manié: emergency thickener, whisked into simmering liquid. Starch slurry: clear, glossy finish for transparent sauces. Blood: dramatic, dark, velvet — never boil after adding.
A roux-based sauce should simmer for at least 20 minutes after thickening to cook out the raw flour taste. The egg yolk/cream liaison can be stabilised with a teaspoon of cornflour for more forgiving reheating. Arrowroot produces a clearer, more elegant finish than cornflour and doesn't break down on reheating. Beurre manié should be added in small pinches, whisked in between additions, until the desired thickness is reached — it's easy to over-thicken. The classical system grades sauce consistency: légère (light, just coating), nappante (coating a spoon), and épaisse (thick, for binding).
Boiling after adding egg yolk liaison — irreversible curdling. Adding roux to cold liquid instead of cold liquid to warm roux (or vice versa — one must be warm, one cold). Lumpy beurre manié from not kneading the butter and flour thoroughly. Using cornflour in a sauce that will be reheated — cornflour breaks down on reheating. Adding blood to boiling sauce — it coagulates into grainy, unappetising lumps.
Le Guide Culinaire — Auguste Escoffier