The effects of different variables in detoxification of a severely inhibiting dilute-acid hydrolyzate by overliming were investigated. Overliming was carried out by increasing the pH to 10, 11 or 12 at two different temperatures, 25 and 60 C, holding the pH and temperature at constant values for different periods of time, 0, 1, 20 and 170 h, and then adjusting the pH to 5.5. All hydrolyzates were then fermented in batch cultivation by Saccharomyces cerevisiae in shake flasks, whereupon one was then selected for continuous cultivation in a bioreactor. The most significant effect of overliming was a sharp decrease in the concentration of furfural and hydroxymethylfurfural, whereas the concentration of acetic acid remained unchanged and the decrease in the total phenolic compounds was less than 30%. Detoxification at pH 12 for more than 1 h was effective, whereas no effect was obtained at pH 10 and the hydrolyzates had to remain at pH 11 for more than 20 h to become fermentable. On the other hand, decrease in sugar concentration during overliming was a serious problem at pH 12, especially at the higher temperature, where up to 70% sugars were degraded. The fermentability of a detoxified hydrolyzate was also tested in a continuous cultivation by immobilized S. cerevisiae in Ca-alginate. The hydrolyzate was fully fermentable at different dilution rates between 0.2 and 1.0 h(-1). (C) 2002 Elsevier Science Ltd. All rights reserved.