What role does sugar play in fruit pie fillings?

Sugar plays several important roles in fruit pie fillings, serving more than just one function. While it certainly enhances flavor by adding sweetness and balancing the tartness of fruits, its interaction with starch is crucial for creating the right texture in the pie filling.

When sugar is combined with starch and heated, it helps to create a thickened filling by absorbing moisture released from the fruit. The presence of sugar also contributes to the viscosity of the mixture, ensuring the filling is neither too runny nor too thick. Furthermore, sugar assists in the gelling process when combined with certain fruits that have natural pectin, further aiding the thickening action.

In addition, while sugar does enhance flavor and can act as a stabilizer to some extent by drawing moisture away and inhibiting spoilage, its primary significant contribution in this context relates to its role in thickening the filling when combined with starch. Hence, its function in a fruit pie filling is multifaceted, but identifying it as a thickening agent when combined with starch is a particularly accurate description of its pivotal role.