The pot ales of malt whisky (MW) and grain spirit (GS) were subjected to batchwise methane fermentation. The pot ale of GS could be more easily treated than the pot ale of MW. The substantial difference in performance seemed to be due to the amount of dextrin. Therefore, the pot ale of MW was first hydrolyzed enzymatically and treated using the same method. As a result, the treatment time necessary for methane fermentation was shortened from 15 d to 11-12 d. Koji mould was cultivated aerobically in the pot ale of MW as a substitute for enzymatic hydrolysis. The dextrin content of the MW pot ale subjected to enzymatic hydrolysis was only 40% of that achieved by cultivation of koji mould. The supernatant of the culture broth was then treated continuously by methane fermentation using a novel upflow anaerobic filter process (UAFP) reactor. A maximum loading rate of 10.8 g/l/d was achieved, corresponding to a treatment time of only 18 h. The residual dextrin in the supernatant of the culture broth was completely decomposed by methane fermentation, as deduced from the elution curve after gel-permeation chromatography.