Combining Ingredients into a Homogeneous Mixture

Two of the major ingredients in cakes—fat and water (including the water in milk and eggs)—are, by nature, unmixable. Therefore, careful attention to mixing procedures is important if this goal is to be reached.

As you recall from chapter 4, a uniform mixture of two unmixable substances is called an emulsion. Part of the purpose of mixing is to form such an emulsion. Properly mixed cake batters contain a water-in-fat emulsion—that is, the water is held in tiny droplets surrounded by fat and other ingredients. Curdling occurs when the fat can no longer hold the water in emulsion. The mixture then changes to a fat-in-water mixture, with small particles of fat surrounded by water and other ingredients.