Roux is cereal flour slightly "fried" in butter, lard, pork fat, or vegetable oil to a variety of light beige colors to thicken gravies and sauces. Basically it is a suspension of flour particles in fat. Thickening is accomplished through its starch contents which gelatinize when cooked in the gravy or sauce. In this frame, flour particles are shown as dark particles along with minute individual starch granules. The image of the same flour suspended in vegetable oil is the same irrespective of the missing frying step. Enhanced optical microscopy. Image width: 3275 micrometers. Magnification: 30.5x if the image is printed 10 cm wide.