Soups and sauces can be thickened in a variety of ways. A sauce must the thick enough to cling to the food, but not so thick it stands up on its own. Starches are by far the most common thickening agent. Cornstarch, arrowroot, waxy maize and the ever popular, roux (roo). But what is a roux and how does it work?

Roux is a cooked mixture of equal parts by weight of fat and flour. If you mix a starch with water, such as cornstarch it is called a slurry

How does it work?

Starches thicken by absorbing water and swelling to many times their original size. This process is called gelatinization. In order for the starch to function at its maximum, each granule of starch must be separated before heating in order to avoid lumps. If granules are not separated the starch on the outside of a lump quickly gelatinizes into a coating that prevents the liquid from reach the rest of the starch inside. This is accomplished in two ways.

1. By mixing the starch with cold water