The aim was to study the crystallization in emulsion process of a hydrophobic cosmetic ingredient (EGDS). The emulsification of the molten EGDS in a continuous phase with the use of an emulsifier in order to obtain a stable droplet size distribution (DSD) is the first stage. The crystallization upon cooling is the second stage. Two optical probes were developed to allow the in situ video monitoring of each stage of the process in real time. From the video sequences recorded the measurement of the DSD was carried out automatically, and by an operator for the PSD. The growth of crystals in motionless droplets was observed under microscope thanks to a thermostated well. The specific power input of stirring was the main parameter acting on the reduction of DSD owing to its action on the droplet break-up mechanism. The surfactant concentration was a parameter of secondary relevance on the DSD (coalescence and stability). The use of a flat blade propeller instead of a Rushton turbine was preferable for the production of a narrower DSD. Finally the time required to reach equilibrium was found higher by a factor of 3-4 than predicted in the literature. It was shown that the droplets crystallized very progressively during cooling, from the biggest to the smallest droplets. With the experimental conditions, one drop gave birth to one particle. The primary nucleation rate was obtained from the analysis of the temporal evolution of the DSD with the hypothesis of a mononuclear mechanism in each droplet. The nature of the mechanism seems to be heterogeneous. Nevertheless its localization in the droplet volume or at the inner interfacial surface was not possible
