What is meringue powder?

Yesterday, I talked about the Cook's Illustrated review of egg white substitutes, which concluded that you are best off working with real, fresh egg whites. The pre-packed, pasteurized egg white substitutes didn't hold up when whipped as well as the real thing. There is one more type of egg white substitute that is known for its ability to whip up, though: meringue powder.

Meringue powder is a mixture of dried, powdered egg whites, cornstarch and gums, which help if bind together. Some powders include sugar, but the majority do not. When mixed with sugar and water, meringue powdered can be reconstituted and beaten to soft or stiff peaks. It can be used to make royal icing, baked meringues, and even angel food cakes, which I have tried with good success. It can not be substituted for egg whites in other recipes, though, only in recipes which call for beaten egg whites. Meringue powders, other than being used for frosting, are best used in recipes where the egg whites would have been uncooked, like in some mousses and sorbets. Keep in mind that meringue powder can have a sort of starchy aftertaste from the cornstarch, so don't reduce the amount of sugar or other flavorings in the recipe you're using unless you want to add another flavor to your dessert.