The flour plays an important role in the texture, structure, and elasticity of an angel food cake. Minimal folding of the flour allows cell walls to form when it comes in contact with the egg protein foam and sugar mixture. If the batter is over-mixed, the egg white proteins may coagulate causing the bubbles to break during baking, or the cell walls may become too rigid, lacking elasticity. This would reduce the volume and result in a coarse texture. However, if the batter is under-mixed, a weak foam will form.