This move, to the air/water interface, by the proteins is also aided by their hydrophobic and hydrophilic part. The hydrophobic moieties orient themselves toward the air while the hydrophilic moieties orient themselves toward the water portion of the interface. The air molecules at the air/water interface interact less with the other molecules that are fully inside the bubble. This lack of interaction causes the air molecules to have excess energy, resulting in surface tension. The presence of egg white proteins at the interface acts as a surfactant which lowers the surface tension and promotes foam development. A foam is a type of emulsion: air in an aqueous solution. If the surface tension was not lowered, the air bubbles would coalescence and the emulsion would separate.