Mechanical leavening

Air can be worked into batters by creaming fat and sugar, whipping eggs, stirring, and even sifting. The trapped air becomes caught within the network of proteins, and the tiny bubbles expand in the oven heat and aid the final lift.

Fat beaten with sugar builds up a structure of air pockets, and the better the creaming, the lighter the cake. Whipped egg whites build a fine network of protein cells that holds a large amount of air, which is why foam cakes such as angel food can rise with little or no other leavener.

Mechanical leavening usually works together with steam and chemical leaveners. Gentle folding keeps the air in the batter once it has been whipped.