eatrightPREP Registered Dietitian (RD) Practice Exam 2026 - Free RD Practice Questions and Study Guide

Roux is a cooked mixture of fat and flour used to thicken liquids like soups, sauces, and gravies. The flour’s starch granules swell when suspended in hot liquid, forming a network that traps water and gives body to the dish. Cooking the flour in fat first also removes the raw flour taste, and you can adjust the color of the roux (white, blond, or brown) to change flavor while still thickening the liquid. This is why its primary purpose is to thicken, not to thin out pastes, preserve fruits, or reduce bitterness.