This paper describes a novel method that makes possible the identification of the nature and the 3D relative spatial position (free or embedded) of the components of complex structures (oil drops, water droplets, air bubbles and multiphase drops) formed in dispersions occurring in fermentation systems, without disturbing (either chemically or physically) the dispersion. Using the refraction index differences between each phase and the image-forming properties of the complex objects formed in addition to the relative size of the bright part of the spheres, it was possible to determine the nature of each type of structure, as well as to discern whether these structures were located inside or outside of the multiphase oil drops. This method allowed determining unequivocally that the small droplets observed within the complex oil drops are part of the aqueous phase and are trapped inside the oil drops, together, in some cases, with air bubbles. (C) 2008 Elsevier Ltd. All rights reserved.