In classic cuisine, demi-glace is a reduced sauce. It's made from brown stock, usually veal bone, and sometimes beef or poultry carcasses and vegetables (celery, onions or leeks, carrot, etc. tomato paste). Thus, it derives its gelatinous texture from the marrow of the bones used in the brown background. And it derives its color from the caramelization of meats and bones before wetting. Sometimes tomatoes and herbs (bay leaf, thyme, parsley, pepper) are added. Demi-glace is the base for many sauces. Depending on the level of reduction, it has different names. When its reduction level is less, it's called Spanish sauce. And when its reduction level is very high, it's called meat ice cream, hence its name demi-glace. In classic French gastronomy, demi-glace is considered the queen of sauces. And in vegetarian gastronomy, she will gladly keep her crown .