The microstructure of ?-gel and ?-crystalline emulsifiers and their effects on cake batter foam have been studied with polarized light microscopy, confocal laser scanning microscopy (CLSM) and image analysis, freeze-etching, and transmission electron microscopy (TEM). The emulsifiers Colco and Aroplus, which are commercial ?-gels, and the monoglyceride Dimodan P in its ?-gel and ?-crystalline forms were added to the batter in concentrations of 0.8, 2.0, 3.1, and 4.2%. Dimodan P ?-gel was also prepared with three NaCl concentrations (0.05, 0.67, and 1.35%c). The distribution of air in the foam was evaluated with density measurements and with image analysis of bubbles in optically sectioned batter. In the cake batter, all the ?-gel emulsifiers decreased the density, thereby increasing the incorporation of air, more than the ?-crystalline emulsifier, which did not have any effect on the density. There were noticeable differences in microstructure between the different ?-crystalline emulsifiers. Large, regular ?-structures seemed to increase the batter volume and interfacial area more than smaller aggregates. Adding salt in the emulsifier gel changed the structure, probably into ?-lamellar liposomes, which impaired the aerating effect at lower concentrations.