Here in the deep Mid-South, our cooking is heavily influenced by the distinctive Creole and Cajun cooking of Louisiana. One of the basic building blocks of these cuisines is the roux, a blend of starch, usually flour, and a liquid fat that’s cooked to varying degrees and used to thicken stews and soups, sauces and gravies. Roux are used in most “Continental” (i.e. European) cuisines as well, and the word itself comes from the French for “red” (rouge).
Starch has been used in kitchens to thicken liquids even before kitchens existed, but anyone who has tried to mix raw flour into a soup to thicken it knows it will just bubble and clump into a wet paste that takes forever to blend. When you combine flour with oil, the starch granules become coated with the fat and blend into stock or milk. Heating the flour in the oil cooks out the raw, pasty flour flavor, and though roux means “red”, roux are cooked for varying lengths of time to different colors for different uses.
Plain flour is most often used for a roux, and it’s the best for general use; save that corn starch for Asian dishes (more about that later). The best rule of thumb is one-part flour to one-part oil in a paste. As to what kind of oil, that depends on what you’re cooking. Generally speaking, if you’re making a white roux, use butter (not margarine, dear hearts). Since butter will burn at higher temperatures, use vegetable oil for darker roux as in most meat dishes and seafood, adding a little olive oil (particularly in a gumbo roux) for added flavor. Use lard or bacon drippings for that authentic down-home flavor you need in biscuit gravy.
Most roux are made in a sauce pan on the stove top. Yes, I know you can make a roux in the oven, or even in the microwave, but the stove top gives you much more control over the product. Cooking a roux on the stove top requires constant care and concentration. A lot of people call roux “Cajun napalm” for good reason; it will stick to your skin and burn, so when you’re cooking roux, avoid any distractions, use long-handled utensils, and for heaven’s sake, keep your children under control or out of the kitchen. Use a skillet with flared sides; cast iron is perfect. Never use a non-stick surface. Some people heat the oil first, some mix the oil and flour together before adding it to the pan, and some keep a mixture of oil/butter and flour in the refrigerator to make a roux on the fly.
Do it your way, but unless you’ve had a lot of practice, don’t use a high heat to make a roux. Cook the roux slowly, and scrape the bottom of the pan to achieve an even color throughout the mixture. If black specks appear, you’ve burned the roux, and you have to throw it away and start over. Never, never, never use a scorched roux; your gumbo, etouffee, or what have you will smell (and taste) like an ashtray.
Just like a slice of bread, a roux will toast; the longer you cook the flour, the darker the “toast”. It smells like popcorn cooking; at least, it does to me. Those of you who grill a lot may be familiar with the Maillard reaction, the reactions of proteins and sugars under heat that give meats and vegetables that roasted flavor. The same process is at work here. Cooking roux to different degrees of browning render different flavor and colors. They also thicken to a greater or lesser degree; the longer you cook a roux, the less it will thicken. You’ll find you will need to add more roux to thicken a dark dish such as a gumbo or an etouffee.
For white sauces—béchamel and other dairy sauce variations—cook the roux only long enough for it to stop bubbling, not long enough for it to brown at all. When making a white roux for soups and gravies it’s better to use slightly more butter, but for a thicker, stiffer sauce such as one you might use to hold a casserole together, use more flour. As a general rule, you’ll use lighter roux for dishes involving poultry or fish, darker roux for beef or game as well as most gumbos with the exception of a file gumbo, which traditionally doesn’t involve a roux at all. With experience, you’ll learn to customize your roux to your cooking.