What is the primary function of a roux in cooking?

The primary function of a roux in cooking is to thicken sauces. A roux is a mixture of equal parts flour and fat, typically butter, that is cooked together to form a paste. When this paste is added to liquid, it helps to thicken the mixture, creating a smooth and velvety texture. The cooking process alters the starches in the flour, allowing them to absorb liquid and swell, which leads to the thickening effect.

While roux can impart some flavor due to the toasting of the flour, its main purpose is primarily structural, serving as a crucial element in classic sauces such as béchamel, gumbo, and gravies. Other functions like emulsifying mixtures or adding color may occur as a secondary result of using a roux, but they are not its primary role in the cooking process.