Washwaters from Spanish-style green olive processing were fermented on a pilot plant scale (500 dm(3)) and evaporated under vacuum. Simultaneous or sequential inoculation in alkaline conditions with Enterococcus casseliflavus cc45 and Lactobacillus pentosus LP99 did not prevent malodorous spoilage. By contrast, appropriate fermentation was achieved when the washwaters were acidified with HCl, to pH S, followed by inoculation with L pentosus, or acidified up to pH 3.4 with no subsequent inoculation. The type of fermentation influenced, to a large extent, the chemical oxygen demand (COD) of the distillate streams obtained when the washwaters were evaporated under vacuum. The high amount of ethanol formed in the washwaters, fermented only by yeasts, gave rise to distillates containing c 30% of the COD originally present in the washwaters, whereas this figure was 10% for washwaters fermented by lactobacilli. This work also disclosed the presence of large amounts of valuable substances, such as lactic acid and hydroxytyrosol in the concentrates, the latter compound being considered a very strong antioxidant with beneficial properties for human health. (C) 2004 Society of Chemical Industry.