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Q. Which is better for thickening: cornstarch or flour? Are they almost always interchangeable? —Ann, Neenah

A. Both cornstarch and flour work essentially the same way. When heated, the starch molecules of each swell up and provide thickening, which is a very desirable texture needed for many preparations. Neither cornstarch or flour is better or worse than the other, but rather which one will work best for the particular cooking application. Cornstarch tends to give an opaque finish and seems to be the preferred thickener for fruit sauces and other preparations where a gel-like finish is desired, like a pie filling or a glaze. Please remember that cornstarch must always be softened with water or other liquid prior to being incorporated or it will irreversibly and undesirably clump together. On the other hand, flour provides a creamier finish, which might be more suitable for thickened soups and gravies. Whether using cornstarch or flour as a thickener, the product being thickened will not achieve its maximum effectiveness until it gets heated thoroughly. Cornstarch needs to reach a temperature of at least 200° F to achieve its maximum thickening, whereas flour will thicken around 150° F (but cooking it a little longer will help minimize its floury taste).