Roux us the principal means used to thicken sauces.
Roux is a combination of equal parts, by weight of flour and fat.
There are three (3) types of roux, as shown as below;
There are two ways to incorporate roux into a liquid without causing lumps.
*Cold stock can be added to hot roux while stirring vigorously with a whisk.
*Room-temperature roux can be added to hot stock while stirring vigorously with a whisk.
Other thickening agents;