A new reflectance technique has been developed to measure the droplet size evolution during the process of emulsification in real-time. This has been used to investigate the dynamic behaviour of 50% oil-in-water emulsions. The performed experiments were designed in order to investigate the occurring droplet break-up and droplet coalescence phenomena individually, by carefully creating processing conditions where each of those events is dominant. The effect of emulsifier (Tween 20) concentration and different hydrodynamic conditions on the droplet break-up and coalescence phenomena and the emulsion droplet size evolution during processing were all investigated. The concentration of Tween 20 was shown to be a key parameter affecting the droplet size of the emulsion at the early stages of processing (within the first 3 min). However, during the later stages of processing, hydrodynamic conditions have a more pronounced effect on determining the final droplet size. Unlike droplet break-up, droplet coalescence rate decreases by intensifying the hydrodynamic conditions of the process as a consequence of the high capillary pressure of the smaller droplets being produced. (C) 2011 Elsevier Ltd. All rights reserved.