How is a Bordelaise sauce typically thickened?

A Bordelaise sauce is traditionally thickened through the method of reducing the liquid. This classic French sauce consists of a rich mixture made from red wine, shallots, bones, and herbs, and it is simmered until the liquid is concentrated in flavor and consistency. This reduction process evaporates water, intensifies flavors, and creates a thick and velvety texture naturally without the need for additional thickeners like flour or cornstarch.

Using techniques such as beating in egg whites or incorporating flour or cornstarch could alter the flavor profile and texture of the sauce, which is contrary to the authentic preparation methods of Bordelaise sauce. The reduction technique ensures that the sauce remains true to its intended depth of flavor and mouthfeel, making this method the most appropriate for thickening it.