The cook who wants to remove the flour from favorite recipes needs to consider the role the flour is playing in that recipe in order to devise a successful substitute. Let's look at the three most common roles played by wheat flour.

In sauces, gravies, soups, and stews, wheat flour plays the role of thickener. When the starch granules in the flour are heated in these dishes, they absorb water, swell, and eventually burst, releasing a starch molecule called amylose that diffuses throughout the solution, trapping additional water and forming a gelatinous network. This is how a few tablespoons of flour turn chicken stock into gravy.

Some thickeners, like cornstarch, are pure starches and contain more amylose than other thickeners, like flour, that contain components other than starch molecules. (Remember, flour also contains proteins and fats, and the starch content is about 75 percent.) Purity affects not only thickening power but performance.

Cornstarch is actually more fickle than flour. For instance, overwhisking pastry cream can break the bonds of the starch gel and thin out the custard. In contrast, the proteins and lipids in flour dilute its capacity to form starch gels, so that more flour is needed for thickening. But these nonstarch compounds also act as binders, ensuring that the liquid not only thickens but also stays that way.

In addition to its use as a thickener, flour can also be used as a coating in dishes like fried chicken or pan­fried pork chops. The starches in the flour are responsible for most of the browning and crisping, while the proteins in the flour help the coating cling to the surface of the food. The proteins also create chew or texture in the fried or baked coating.

Finally, the main use for flour in the home kitchen is as a structural agent in baked goods. It’s here that the gluten performs an essential function; the ability of the proteins in wheat flour to expand and trap gas bubbles is key in many baked goods.

In a baked good such as a muffin, the starch granules in the flour absorb moisture and swell as the batter is being prepared. The strands of gluten bond together and surround the starch granules. Gluten is particularly elastic and strong, especially when heated. This highly organized and strong network of gluten gives the muffin its structure and shape.

Compared with wheat flour, gluten­-free flours generally contain less protein, so they don’t do as good of a job of organizing and holding the swollen starch granules. These proteins are also less elastic than gluten. In order to replace wheat flour with a lower­protein flour, such as rice flour, you must boost the effectiveness of that protein.