By Harold McGee
In cake making, the mixing step doesn’t just combine the ingredients into a homogeneous batter: it has the critical purpose of incorporating air bubbles into the batter, and thereby strongly influencing the final texture of the cake. The various ways of aerating the batter help define families of cakes (see box). They involve beating the sugar and/or the flour into the fat, the eggs, or all the liquid ingredients. The fine solid particles carry tiny air pockets on their surfaces, and the particles and beating utensils carry those pockets into the fat or liquid. Flour is often added only after the foam is formed, and then by gently folding it in, not beating, to avoid popping a large fraction of the bubbles, and to avoid developing gluten. (For folding as a mixing technique.) Mixing the dry flour and fat together also prevents the gluten proteins from bonding strongly to each other.