The production of cellulosic ethanol involves three major sequential steps: (i) the chemical and physicochemical pre-treatment of the lignocellulosic biomass, (ii) the hydrolysis of cellulose and hemicelluloses to fermentable sugars by cellulolytic enzymes, and (iii) microbial fermentation for the production of ethanol. Regardless of the process used for pre-treatment, various toxic compounds (weak acids, furan derivatives, and phenolics) are produced during pre-treatment that inhibit microbial growth, metabolism and ethanol yield 4 and 5. In addition, high temperature and concentrated ethanol are potent inhibitors of industrial lignocellulosic hydrolysate fermentation, which results in reduced growth and ethanol yield 6 and 7.