Oil-in-water emulsions composed of methyl ricinoleate (MR) or castor oil (CO) as the organic phase, stabilized by Tween 80, are in the basis of the biotechnological production of gamma-decalactone. Yarrowia lipolytica was used due to its ability to grow on hydrophobic substrates and to carry out the biotransformation. The characterization of oil droplets size distribution by laser granulometry was performed under different oil concentrations. The impact of the presence of cells on droplets size was also analyzed as well as the relevance of washing inoculum cells. Furthermore, the granulometric characterization of the emulsions was related with gamma-decalactone production and it was observed that, in the presence of non-washed cells, the smaller droplets disappeared, using both oils, which increased gamma-decalactone concentration. Thissuggests that the access of cells to the substrate occurs by their adhesion around larger oil droplets.