demi-glace, traditional brown sauce of French cuisine that is used on its own or as the flavouring base for other sauces, soups, and stews.
The sauce stems from sauce espagnole, a classic brown sauce and one of the five “mother sauces” of French cuisine (béchamel, velouté, espagnole, hollandaise, and tomato) from which other (“daughter”) sauces are made. Demi-glace is made with a brown stock that begins with roasted ox, veal, or beef bones, to which are added tomato puree, red wine, mirepoix, other aromatic vegetables such as garlic and leeks, and herbs and spices such as thyme, pepper, and bay leaves. The mixture is briefly brought to a boil and then cooked on low heat for as long as 24 hours, skimming the fat and adding water as needed and then straining the stock to remove some of the solids while retaining the gelatin from the bones.
Demi-glace takes this cooking a step further, not adding more water at this point but instead reducing the stock by about half, lending it its name—which means “half-glaze,” a sauce not thick enough to serve as a true glaze—and yielding a rich, meaty, brown, gravylike substance. It is not a gravy, however, which is thickened with a roux (a mixture of flour and fat). Instead, demi-glace is the essence of the stock, gelatinous and shimmering. Reducing the demi-glace still further to a syruplike consistency results in a glace de viande, or “meat glaze.”
In France and in fine dining establishments throughout the world, making demi-glace and other sauces is considered a critical test of a chef’s skills. Demi-glace can be eaten as is, but in haute cuisine it is typically used as a base for other meat sauces or even gravy, with a spoonful or two added to dishes to deepen their flavour. Demi-glace can be frozen in ice trays, with cubes used in this way. Because it is time- and labour-intensive, many home cooks today, even in France, prefer to purchase ready-made demi-glace.