When it comes to making your own gravy, you may have a preference as to which type of thickener you use. The most basic method of making gravy uses a wheat flour slurry (a mixture of flour and water) or a wheat flour and butter roux to thicken the pan drippings when you cook a chicken, turkey, or roast. But you can substitute the flour with some other starches, including cornstarch and arrowroot. Each thickener will result in a slightly different texture and appearance when it comes to the finished gravy.
Since most home cooks stock all-purpose wheat flour in their pantries, using flour to thicken gravy is quite convenient. You can incorporate the flour into the gravy by first mixing it with water (called a slurry) or by cooking it into a roux. When making a roux (pronounced "roo"), you cook the flour and some butter together until it reaches your desired color—a lighter roux would be more appropriate for white or country gravies, while progressively darker hues are ideal for turkey, chicken, and beef gravies.
Do keep in mind, however, that flour adds a cloudy appearance to the gravy, so it may not always be the best choice. It also does not have the same thickening power as other starches and needs to boil for about 3 minutes to reach the proper consistency. Some styles of gravies and sauces don't benefit from the high temperature and longer cooking time required to do this, so using flour as the thickener may not work for certain recipes.
Flour varieties other than wheat do not have the same starch content, so not every flour makes an appropriate substitute for wheat flour as a gravy thickener. A good alternative is sweet rice flour, which seems to consistently perform in place of wheat flour as a gravy thickener.
Chinese and other Asian recipes frequently rely on cornstarch to thicken sauces because adding this thickener results in a lighter, more translucent gravy with a glossy sheen. To use cornstarch as a gravy thickener, start by making a slurry of equal parts cornstarch and cold water, stirring until it looks completely smooth. Then slowly incorporate it into the pan drippings, whisking continuously. Cornstarch turns lumpy in hot liquid, so don't skip the slurry step, and be sure to add it slowly while you whisk to thoroughly integrate it into the drippings.
Keep in mind the starchy flavor can linger unless you cook it long enough, so simmer the gravy for a minute or two after you add the slurry. Be careful not to overcook it, though, which can cause it to turn runny. Remove a cornstarch-thickened gravy from the heat before you add acidic ingredients. One tablespoon of cornstarch thickens 1 1/2 to 2 cups of gravy.
Arrowroot is a nearly flavorless starch processed from the fleshy tropical plant of the same name. Using it as a thickener results in a smooth, transparent gravy with a light texture. Arrowroot does not require cooking to remove a raw taste and makes an excellent choice for sauces using eggs or other ingredients that should not be boiled since the mixture thickens below the boiling point.
Gravy thickened with arrowroot does not hold well, however, and you cannot reheat it. You should finish your gravy with an arrowroot slurry no more than 10 minutes before you plan to serve the meal. Extended high heat and vigorous stirring nullify the thickening properties of arrowroot; if your gravy suddenly turns soupy, you've gone too far. Use 2 1/2 teaspoons of arrowroot per 1 cup of cold liquid for a medium-thick sauce.