Carême made a number of contributions to this progress, and perhaps the most notable involved the sauces. His idea, set forth in The Art of French Cooking in the 19th Century, was to organize the infinity of possibilities that Marin foresaw, and thereby help cooks realize them. He classified the sauces of the time into four families, each headed by a basic or leading sauce, and each expandable by playing variations on that basic theme. Only one of the leading sauces, espagnole, was based on expensive, highly concentrated meat extract; both velouté and allemande used unreduced stock, and béchamel used milk. Many of these sauces were thickened with flour, which is much more economical than reduced meat bouillon. This approach suited the limits and needs of postrevolutionary cuisine. The parent sauces could be prepared in advance, with the novel but minor modifications and seasonings to be done at the last minute on the day of the meal. As Raymond Sokolov puts it in his guide to the classic sauces, The Saucier’s Apprentice, these sauces were conceived as “convenience foods at the highest level.”