Meringue kisses

Meringue kisses are small meringue cookies. Their base is common (French) meringue, which Anna Olson's Back to Baking describes as egg whites, brought to room temperature and beaten with a small amount of sugar. It can be baked until crisp in a low-temperature oven and made into simple cookies.

The science is that of an egg-white foam stabilized by heat. A Dickinson College chemistry page explains that the whites are mostly water with some protein, that yolks must be kept out because their fat disrupts the foam, and that whipping traps air in bubbles wrapped by the proteins. Cream of tartar, an acid, helps the foam stay stable, and sugar is added slowly after the whites begin to foam, until stiff peaks form that hold their shape.

Over-beating separates water from the foam and gives a grainy mixture that will not shape well.