The performance of fermentation bioreactors is strongly related to the oxygen transfer from air bubbles to microorganisms to improve their growth. The action of the bubbles helps mix the reactor and also strips out waste gases (carbon dioxide). However, accurately characterizing the gas-liquid mass transfer in such processes is still a challenging issue, mainly because of the liquid phase complexity. The aim of this project is to develop specific techniques and rigorous models to better estimate the various mechanisms that govern the mass transfer process locally. New visualization techniques are proposed to estimate the local dissolved concentrations of both gases simultaneously. A new model will enable the fermentation processes to be adapted and their energy consumption to be reduced.