Meringue powder and cream of tartar can be used as stiffening agents in recipes. Meringue powder tends to be used more rarely, sticking to use in meringues and royal icing. Cream of tartar is used to stiffen egg whites, for gingerbread house icing or with baking soda.
Meringue powder is a white powder made from dried egg whites, cornstarch and food gums. The main ingredient is the egg whites, as they help make a stiff frosting or meringue topping. The cornstarch keeps the meringue powder from clumping together while stored.
Cream of Tartar
Cream of tartar, known scientifically as potassium bitartrate, is an acid salt used in several cooking recipes. When tartaric acid is halfway neutralized with potassium hydroxide, the acid is turned into a salt, known as cream of tartar. Grapes are a natural source of tartaric acid and the sediment produced from wine making is used to make cream of tartar.
Meringue Powder Uses
Meringue powder has limited uses, primarily in royal icing or a meringue. Royal icing has more stability than other icings so it can be used to form cake decorations that won't fall apart. You can use meringue powder as an egg white substitute in some recipes but it will change the taste of the recipe. Don't try to substitute meringue powder for a recipe that doesn't call for stiff egg whites as the effects won't be the same. Angel food cake or mousses can use meringue powder if absolutely necessary but they won't taste quite as good as with egg whites. Use 1 tbsp. of meringue powder mixed with 2 tbsp. of water is the equivalent of one egg white.
Cream of Tartar Uses
Cream of tartar is primarily used with non-acidic foods (egg whites, milk and baking soda) to activate the food in a recipe. In candy and frosting recipes, cream of tartar is used to create a creamy texture because it keeps sugar crystals from forming. Gingerbread house icing uses cream of tartar since the frosting hardens faster and holds the house together. You can also use cream of tartar with egg whites to stabilize the whites and cause them to stiffen faster. Other recipes that use baking soda, a non-acidic ingredient, add cream of tartar to activate the baking soda in the dish.