What is commonly added to whipped egg whites to help increase volume, along with pectin?

Adding cream of tartar to whipped egg whites serves an important purpose in increasing their volume and stability. Cream of tartar is an acid, specifically potassium bitartrate, which helps to stabilize the proteins in egg whites as they are whipped. When egg whites are whipped, the proteins unravel and form a network that traps air, creating the desired foam. The presence of cream of tartar strengthens this protein network, preventing the foam from collapsing and allowing it to hold a greater volume.

While sugar is often added to achieve a sweet flavor and can also help stabilize the foam when added at the right time, cream of tartar specifically contributes to the structural integrity of the meringue. Salt and milk would not provide the same beneficial effects; salt can actually weaken the protein structure if added too early, and milk would alter the composition of the egg whites, potentially interfering with their ability to whip. Thus, cream of tartar is the most effective ingredient in this context for enhancing the volume of whipped egg whites.