BACKGROUND: The baker's yeast industry is a major market and due to the intensified production large quantities of waste are generated. Wastewater from the baker's yeast industry with high content of molasses was treated anaerobically in an upflow anaerobic sludge blanket (UASB) reactor for the production of methane (CH4). RESULTS: The molasses wastewater obtained from industry had a high pH value around 8.0 +/- 0.5, which remained constant during the experimental period. The system was operated at anorganic loading rate (OLR) of 2.4-7.65 g of volatile solids per liter per day (g VS L-1 d(-1)) and the best results were observed at 4 g VS L-1 d(-1), where methane production exceeded 350 L CH4 kg(-1) VS. Anaerobic chemical oxygen demand removal was also examined and it was found that for the latter conditions of optimum OLR, it was more than 35%. VFA analysis revealed that acetic acid concentration in the reactor was more than 25 mmol L-1 even under optimum conditions. CONCLUSIONS: The tested hydraulic retention time (HRT) values did not affect methane production, unlike the OLR. The increased acetic acid concentration in the UASB reactor and the high pH were credited to the inhibition of aceticlastic microorganisms. (C) 2016 Society of Chemical Industry