A roux is a blend of equal parts of flour and fat. It is used as the base for sauces and gravies as well as to thicken soups and stews. The mixture is cooked to different stages depending on how it will be used in a recipe and should have the consistence of very thick batter.
Making a Roux
Fats suitable for use in making a basic roux include all vegetable-based cooking oils, olive oil and butter; rendered animal fats are often used to make pan sauces and gravies. Because butter contains water, the roux will require a slightly longer cooking time to thicken, and it should be completely melted before adding the flour. The 1-to-1 ratio of oil or melted butter to flour produces a thick paste that thickens any liquids added to it, providing a sauce base for dishes such as macaroni and cheese and chicken a la king. A darker roux is best made with oil, as it can be cooked at a higher temperature than butter without burning.
When making a roux, you can cook it to varying degrees of darkness, from white and pale brown to medium brown and dark brown. This versatility enables roux to thicken light sauces for dishes featuring poultry, fish or pasta, or deeply colored sauce for dishes such as meat stews, meat gravies and gumbos. Cooked over medium heat, a white roux takes about two minutes to prepare, while a light brown roux requires about 10 minutes. A medium roux takes about 15 minutes to prepare, while achieving a deep brown roux with a characteristically nutty flavor can take up to 1 hour of cooking time.
A roux is the first step in the cooking process for making a basic white sauce. Called a béchamel sauce, it involves hot milk added slowly to a simple white roux that has not been cooked beyond the first stage. A béchamel sauce is traditionally made with butter and flour and not allowed to brown, which makes it ideal as a base for cheese and other sauces where a light coloring is desired. A light roux is also the basis for sausage gravy, which incorporates sausage drippings into the sauce instead of oil or butter. As a general rule, a roux made using 2 tablespoons each fat and flour thickens about 1 1/4 cup of liquid.
It's important to keep in mind that the type of fat used in a roux affects its flavor, particularly if it is used in a mildly flavored sauce. In addition to oil and butter, a roux can be made with other fats, including lard, shortening, bacon fat or the pan drippings left after roasting any type of meat. The same ratio of fat to flour applies, which means that you will need 1/4 cup of flour for every 1/4 cup of melted fat. A roux made with vegetable shortening will be bland and tasteless, while one made with bacon fat will impart the smoky bacon taste.
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