A film of sizing agents protects yarn during weaving. Its removal in a subsequent washing process causes 50% of the organic effluent load of textile finishing processes and requires large amounts of auxiliary chemicals (e.g., surfactants). Microbial desizing is a new bioprocess that uses the acidifying culture of a two-phase anaerobic digestion plant for the removal and partial degradation (acidification) of the sizing agent. Soluble starch is used in this study to characterize the enzymatic properties in the supernatant of the desizing culture and to link them to desizing efficiencies. The supernatant of the culture (grown at 37 degreesC, pH 5.5) displayed the highest enzymatic activity between pH 4 and 5 and in a broad temperature range (20-80 degreesC). Highest metabolization rates were determined with the substrate amylose. Short chain dextrins (average of 5 and 10 glucose units) and amylopectin were converted significantly more slowly. At 37 degreesC the half-life time of the enzymatic activity in the supernatant was 45 h. In a desizing test a decisive reduction of the chain length was found already after 1 h (allowing starch solubilization). A microbial desizing experiment with dyed, native maize starch demonstrated the efficiency of the proposed bioprocess.