In general, the highest consumption of glucose occurred during the first 6 h of fermentation and the decrease in glucose concentration coincided with an increase in ethanol production. Regardless of the conditions used for pretreatment, the amount of glucose available for fermentation was higher in water-washed substrates and this explains why their ethanol yields was higher than that of unwashed substrates. Also, after 6 h of fermentation, the consumption of glucose remained stable until it was exhausted from the medium and, at this point, the ethanol yield stabilized as well. The concentrations of xylose (Fig. 3) remained constant during the entire fermentation process for both unwashed and water-washed substrates because the yeast was not able to ferment it. And as mentioned before, unwashed substrates generally exhib- ited higher amounts of xylose in the fermentation medium, com- pared to experiments carried out with water-washed substrates.