Air cells in cake batters are important for texture and for leavening. A fine, smooth texture is the result of small, uniform air cells. Large or irregular air cells result in a coarse texture. Also, you will recall from that air trapped in a mix helps leaven a cake when the heat of the oven causes the air to expand. When no chemical leavener is used, this trapped air, in addition to steam, provides nearly all the leavening. Even when baking powder or soda is used, the air cells provide places to hold the gases released by the chemical leavener.
