A method for obtaining a fermentation product from a sugar hydrolysate obtained from a feedstock containing hemicellulose, by (i) removing suspended fiber solids from said sugar hydrolysate to obtain a clarified sugar solution; (ii) fermenting xylose in the clarified sugar solution in a fermentation reaction with yeast to produce a fermentation broth comprising the fermentation product; (iii) separating the yeast from the fermentation broth to produce a yeast slurry; (vi) treating the yeast slurry thus obtained with an oxidant to kill microbial contaminants, thereby an oxidant-treated yeast slurry; (v) re-introducing at least a portion of the oxidant-treated yeast back to step (ii) to increase the concentration of yeast in said fermentation reaction; and (vi) recovering the fermentation product.