The effect of the mineral kissiris on the fermentation of sucrose solutions in an Up-Flow Plug Anaerobic Bioreactor (UPAB) was examined. Increased acid generation and a decrease in the time needed for the start-up of the process were obtained. Biogas was produced at volatile fatty acid (VFA) concentrations of 10.48-17.72 g/litre and at a pH close to 6. Loadings in the range of 13.3-37.4 g COD/litre/day and 43-68% COD removal efficiencies after a day were also obtained. In the absence of kissiris no methane fermentation was produced.