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By James Peterson

Published 1991

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The most common method for thickening liquids with flour is to prepare a roux by cooking the flour with an equal volume of butter. This attenuates the flavor of the flour and eliminates lumps. Hot liquids are then added to the cooked roux, and the mixture is brought to a simmer until it thickens. Because flour contains proteins and other compounds that impart flavor, sauces thickened with roux are usually skimmed for at least 30 minutes once they have been brought to a simmer to eliminate impurities. Although stock that is used for sauce making should be carefully skimmed and degreased before it is combined with roux, further skimming is necessary once the roux has been added, to eliminate the butter and to remove impurities in the flour.

One excellent method for using flour is to cut the amount called for in classic sauces by half and then reduce the thickened sauce carefully to the desired thickness. This method allows more time for skimming and degreasing and will attenuate any floury taste.

Both white and brown roux are used in classic French cooking. White roux is used for white sauces, brown roux for espagnole, the traditional base for the classic brown sauces. To prepare brown roux, the flour is either cooked for 15 to 20 minutes in clarified butter or browned first in the oven and cooked with butter in the same way as white roux. Brown roux is rarely seen in modern restaurant kitchens.

To prepare roux, use a whisk to stir together equal volumes of butter and flour in a saucepan over medium heat. Bring the liquid to be thickened (such as stock or milk, for velouté or béchamel, respectively) to a simmer in another pot. Cook the roux for about 5 minutes, until it has a pleasant toasty smell, and then remove the saucepan from the heat for a minute to let the roux cool. Return the pan to the heat and pour in the hot liquid while whisking. Continue whisking until the sauce comes to a simmer. Turn down the heat and slowly simmer the sauce for 30 minutes. Skim any froth and impurities from the sauce’s surface with a ladle. It is also possible to thicken liquids with roux by simply adding the cold liquid to the hot roux, thus saving time and a pot. When using this method, however, be careful to whisk thoroughly to prevent lumps.