For what purpose is starch primarily used in pie fillings?

Starch is primarily utilized in pie fillings as a thickening agent. When heated, starch granules absorb moisture and swell, which results in the thickening of the filling's liquid content. This process helps achieve a desirable texture and consistency in the filling, ensuring it holds its shape when baked and served. Proper thickening is crucial, as it contributes to the overall quality of the pie, preventing it from being too runny or soupy.

Regarding the other options, while flavor is essential in pie fillings, starch does not enhance it; it serves a functional role only. Similarly, aesthetic color is also not a function of starch, as it is usually a neutral ingredient that becomes clear or translucent upon cooking. Lastly, enhancing shelf life is not a primary characteristic of starch in this application; there are other methods and ingredients specifically designed for preservation. Thus, using starch to thicken is the most accurate and relevant function in the context of pie fillings.