Lactobacillus cellobiosus, isolated from city wastes, produced an extracellular alpha-amylase and produced lactic acid by direct fermentation of waste potato mash. Using a 5% (w/v) potato mash with 3% (w/v) CaCO3 to neutralise the lactic acid produced, 50% conversion of starch to lactic acid occurred in 48 h without any other media supplement.