Within the context of biomass biorefining, valorisation of residual streams for energetic and/or material use is gaining increasing attention. Among other processes, anaerobic digestion has been extensively used for the production of methane from organic waste. Acidogenic fermentation (acidogenesis) is mainly studied as an intermediate stage of anaerobic digestion for the optimisation of methane production, but it could be also seen has a stand-alone process for the production of chemicals like volatile fatty acids (VFA: organic acids with a carbon number C2-C6). VFA can be used as building blocks for the "green" chemistry (e.g. solvents, aromas), for the production of biofuels, for the production of bioplastics (i.e. polyhydroxyalkanoates) or as susbstrate for biological nutrient removal. Our research focuses on the acidogenesis of agroindustrial residues with a complex composition (e.g. fruit pulps, brewery residues) by natural, mixed microbial populations (e.g. sludge, ruminal juice) for the selective production of VFA. The challenge is to master the experimental conditions in order to get the desired fermentation profile, while considering the complexity of both the substrate and the microbial consortium. Fermentation of agroindustrial residues provided total VFA (tVFA) concentrations in the range of 15-20 gCOD/kg_fermentation liquor and conversion yields in the area of 0.25 gCOD_tVFA/gCOD_substrate. Butyric and acetic acid were the predominant VFA