Emulsifying

Egg yolks are effective emulsifiers, meaning that they can keep oil and water in emulsions from separating. Egg yolks are particularly effective at emulsifying because of their lipoproteins and emulsifiers, including lecithin. Without this ability, eggs would not be effective at binding ingredients in batters and doughs.

Eggs are generally added to creamed butter or shortening. This emulsifies and stabilizes the mixture, and helps to blend it with the rest of the ingredients. Care must be taken when adding eggs to creamed shortening. If eggs are added too quickly or while still cold, the emulsion breaks. While the subsequent addition of flour and other ingredients appears to bind the emulsion back together, a poorly emulsified batter bakes into a cake that may not rise properly and that has a coarser crumb.