The waste of beer fermentation broth was evaluated as a basal medium for the production of water-soluble oligosaccharides (WSOS) by Gluconacetobacter hansenii PJK. The broth was tested at various dilution ratios in a flask culture and the undiluted broth was determined to be the best for the WSOS production. The undiluted waste of beer fermentation broth was subsequently used in a jar fermenter for a batch culture, at various impeller speeds. The production yield of WSOS increased with an increase in impeller speed and it reached 112.65 g L-1 at 600 rpm after cultivation for 240 h. The maximum yield of WSOS obtained in this study was almost 100 times more than that with a defined medium using the same strain. This study revealed that the waste of beer fermentation broth is a feasible, inexpensive and worthy medium for the production of WSOS. (C) 2007 Elsevier Inc. All rights reserved.