A common ingredient in custards, sauces, soups, pies and puddings, cornstarch is typically used as a thickening agent. Because it's free of proteins, cornstarch is clear when heated, so it doesn't affect the color of your food. If you're out of cornstarch or want to avoid it because of a corn allergy or concern over genetically modified corn, use a substitution.
Like cornstarch, all-purpose flour is an excellent thickener. Because it contains protein, flour becomes slightly opaque when you heat it, and it will thicken more slowly than cornstarch. Choose flour as a substitute for cornstarch if you're preparing gravy, stews, white sauces or pies with apples or pears. If you're making something like a berry pie where you want the thickened filling to be clear, flour isn't your best option. If you're preparing a stove-top recipe, you'll have to cook the flour to get rid of its raw, floury taste. After adding the flour to your gravy, sauce or other dish, let it boil for approximately 3 minutes.
Like cornstarch, arrowroot is gluten-free. This flavorless thickener, which works even at low temperatures, turns clear and shiny when heated. Arrowroot doesn't keep well and will lose its thickening power after about two months of storage. When heated for long periods of time, arrowroot will break down and start to thin out. It also doesn't work well with dairy ingredients: It can turn a bit slimy.
For desserts like pies, puddings and baked custards, quick-cooking or instant, tapioca is a thickener with a slight jelly-like consistency and somewhat chewy texture. It works particularly well with ingredients such as berries and peaches that contain a lot of liquid. If you're making a pie with a lattice crust or numerous vents, pass the tapioca through your food processor before adding it or use tapioca flour. The food processor breaks up the small tapioca granules even further so they'll dissolve completely.
Potato Starch and Flour
Depending on what you're preparing, potato starch or flour can make suitable substitutes for cornstarch. Both of these ingredients are gluten-free and produce clear, glossy sauces. Potato flour has a rather strong potato flavor, which potato starch lacks, making it unsuitable for use in desserts and delicate sauces. Potato starch, however, works well in delicate sauces and, thanks to its quick thickening action, can be added near the end of the cooking time to fix a sauce that turned out too thin.
If you're using arrowroot, potato starch or potato flour as a cornstarch substitute, use equal amounts in your recipe. If your recipe calls for 1 tablespoon of cornstarch, use the same amount of your substitute ingredient. For all-purpose flour or quick-cooking tapioca, use twice as much of the substitute. If your recipe calls for 1 tablespoon of cornstarch, use 2 tablespoons of flour or tapioca.