Sustained oscillations were observed in continuous very high gravity (VHG) ethanol fermentation by Saccharomyces cerevisiae, in which medium containing sugars in excess of 250 g/L was fed and more than 15% (v/v) ethanol was obtained at the end of the fermentation.Compared with steady state presented by continuous ethanol fermentation under regular fermentation conditions.Ethanol inhibition and osmotic stress were postulated to be key factors triggering this phenomenon.