Lecithin

Found in egg yolks, lecithin is a type of emulsifier called a surfactant. One end of a surfactant molecule dissolves in fat and the other end in water such that the two are held together into an emulsion. Lecithin comes in both liquid and powdered forms. The liquid is best dissolved into fats that are later to be emulsified, while the powder is best for making foams. Both forms are used in concentrations of 0.5% to 3% of the fat they are emulsifying.