Time for a little culinary chemistry lesson. When air is incorporated into a liquid or gooey solution, air bubbles are entrapped and create a foam. If the foam is stabilized by proteins, it leavens a food – which increases its height and reducing its density.
An egg’s viscosity is ideal for incorporating air cells during the whipping or beating process. By doing so, air bubbles decrease in size and increase in number. Egg whites specifically are able to create the largest possible food foam (6-8 times greater in fact). Cream of tartar, which is an acidic salt, can be added to lower the pH of the egg white. This can help to stabilize the foam. (ex. Angel food cake)
Eggs are also a great asset in the whipping process itself. Egg yolk solids actually increase the rate of whipping. Sweetening with 10% sugar or corn syrup before being frozen or dried improves the rate of whipping even more. This can be extremely beneficial when dealing with slow-whipping mixes, and for ice cream in particular.