Which ingredient adds a tangy flavor while increasing the volume of whipped egg whites?

The ingredient that adds a tangy flavor while increasing the volume of whipped egg whites is cream of tartar. This substance is an acid, technically known as potassium bitartrate, which helps stabilize the egg whites when they are whipped. The presence of cream of tartar increases the volume of the whipped egg whites by allowing them to hold air more effectively, resulting in a lighter and fluffier texture in baked goods.

In addition to its stabilizing properties, cream of tartar imparts a slight tanginess to the flavor profile of the final product. It is commonly used in recipes for meringues, angel food cakes, and other desserts where egg whites need to be whipped to achieve a specific structure.

While citric acid is also an acid and can add tanginess, its primary function is not necessarily related to stabilizing egg whites in the same way cream of tartar does. The other options, such as baking soda and sugar, do not provide the same combination of stabilization and tangy flavor that cream of tartar offers. Baking soda acts as a leavening agent and requires an acid to activate it, while sugar contributes sweetness and can slightly stabilize whipped egg whites but not to the extent of cream of tartar.