Some ingredients in cake recipes, such as eggs and oil, are emulsifiers in themselves. Emulsifiers perform a variety of functions. Their chemical interactions and reactions serve to break up fat into smaller particles, coat the fat particles to prevent them clumping, allow for the even distribution of these particles throughout another substance, and aid in the extended stabilization of fat, water and protein so as to create a smoother, more consistent and moister crumb.

Lecithin, derived from soy, present in soybean-based vegetable oil, is a natural emulsifier that moistens and improves the overall texture of cakes and baked goods. Cake recipes call for vegetable oil precisely for this reason, as do store-bought cake mixes. Lecithin is unique in that it contains substances that are both hydrophillic and lipophillic -- equally suspended in both fat and water simultaneously. Lecithin's ability to evenly fuse fat and water combinations accounts for its emulsifying properties. Because cake batter is an oil in water mixture, any cake batter to which lecithin is added receives the benefit of lecithin's function.

Store-bought yogurt and sour cream contain synthetic emulsifiers. It's possible to "borrow" the emulsifying properties in these foods by adding them to cake batter. Muffins and cakes with added yogurt or sour cream are moister because of the added fat, the emulsifiers used in these products, and their ability to promote a creamier consistency. There are no hard rules or recommendations for adding exact amounts of yogurt or sour cream to cake recipes, though 1/2 to 1 1/2 cups are the most common measurements.

To use egg-based lecithin, add room temperature yolks one at a time to creamed butter and sugar while whisking or mixing constantly. Completely mix in each egg yolk before adding the next one. Lecithin intended specifically for baking is available in liquid and granular form. Substitute a small portion of the overall amount of required oil with lecithin, and add the remaining oil as well. Blend the cake batter well to sufficiently emulsify all the ingredients. Add 1 to 2 tablespoons of granular lecithin per 3 cups of flour.