Cornstarch and tapioca starch thicken gravies, puddings and sauces. Cornstarch can be found in the baking aisle of grocery stores and can be mixed with flour to create moist cakes and cookies. It can, however, leave a chalky aftertaste in food or turn gummy if the food is chilled. Should you want to avoid corn-based products, you can substitute tapioca starch. The substitution amounts may vary, so you need to know the proper conversions.
Read the amount of cornstarch called for in your recipe.
Double the amount of cornstarch called for when used as a thickening agent for gravies and other sauces. Use that doubled amount as the measurement for your tapioca starch. For instance, if your recipe calls for 1/4 cup of cornstarch, use 1/2 cup of tapioca starch. Stir the tapioca starch in an equal amount of cold liquid until smooth, then add the starch mixture to the hot gravy or sauce. This helps ensure smoothness and no clumping.
Thicken pie fillings in the same way, using twice as much tapioca starch as cornstarch called for in your recipe. Mix the tapioca starch into the pie filling, and allow the filling to sit for 15 minutes before pouring it into your pie shell and baking. This allows the tapioca to soak up some of the filling juices and results in a smooth, even filling.
Use an equal ratio in baking recipes. For example, if your recipe calls for 1/2 cup of cornstarch, substitute 1/2 cup of tapioca starch. In baking, the ratio of dry ingredients to wet ingredients, such as eggs or milk, is important to a successful final product. If you add more dry ingredients than the original recipe calls for -- 1/2 cup of starch instead of 1/4 cup, for example -- your final product will turn out differently than intended.
Tapioca starch can be purchased at some grocery stores and at specialty baking stores or health food stores. Pearl tapioca can be finely ground in a spice grinder to create tapioca starch.