Skimming and dépouillage

Dépouillage is the classical French practice of clarifying a stock or sauce by drawing off its impurities as they rise, and it belongs to the codified brigade kitchen described in Larousse Gastronomique and in Escoffier's Le Guide Culinaire. It is carried by the saucier and the cook in charge of the fonds, for whom a clear, bright stock is the foundation of every sauce built upon it.

Skimming (écumage) removes the grey coagulated protein and the fat that rise to the surface of a pot of bones, meat or vegetables as it comes to the simmer, using a skimming ladle (écumoire) or a flat spoon. Dépouillage is the longer treatment of a sauce, above all the sauce espagnole and its derivatives, which is kept at the barest simmer to one side of the heat so that a skin forms on the cooler side. The cook lifts away the fat and impurities gathered there, repeatedly, over several hours, until the sauce is glossy, clear and lightly bound. Cold water is sometimes added to a stock at intervals to check the boil and bring the scum up again, so that it can be drawn off.

A properly skimmed fond or sauce carries a clean, rounded flavour and a gloss that lets the principal ingredient speak, so it accompanies roasts, braised meats and game in the form of a demi-glace or a jus lié. It is served with the red wines of the same region as the dish, for the structure and tannin of such a wine meet the gelatinous body of the sauce. Impurities left in would add bitterness and cloudiness that blunt both the sauce and the wine beside it.