Have you had an angel food cake before?
Angel food cake is a cake made of egg white, sugar and flour. The egg whites are beaten until stiff foam is formed. Sugar is added not only for the sweetness of the cake but also to stabilize the foam by incorporating air into the mixture. Nonetheless, adding too much sugar could cause the cake to collapse.
In order to get the optimal tender texture of the cake (fine grain, light spongy texture and high volume), the ingredients must be at room-temperature. The egg white must be beaten in a non-greasy and dry mixing bowl (metal bowl is preferred).
Cream of tartar is routinely added to an angel food cake. Cream of tartar is an acid which strengthens the egg white foam.
It strengthens the foam by denaturing the protein in egg white and therefore stabilizing the air cell structure.
The acidic nature of cream of tartar also contribute to the softness and white colour in the angel food cake by whitening the flour’s natural yellowish, anthoxanthin pigments.
BROWN, A. 2004. Understanding Food Principles and Preparation, Thomson Wadsworth.