The aim of this investigation was to attain high ethanol concentration by concentrating sweet sorghum juice using a two-step membrane separation process. Ultrafiltration permeation of the juice was used to remove residues, followed by nanofiltration concentration to increase the sugar concentration. The concentrated juice containing 180.0 g L-1 sucrose, 59.3 g L-1 glucose and 49.3 g L-1 fructose supplemented with nitrogen sources (10 and 20 g L-1 of yeast extract and polypeptone, respectively) was fermented by Saccharomyces cerevisiae BY4741 to produce 133.5 g L-1 of ethanol (87.6% of theoretical yield) after 48 h fermentation. Importantly, the addition of lower concentrations of exogenous nitrogen sources (3 and 6 g L-1 of yeast extract and polypeptone, respectively) or no exogenous nitrogen sources resulted in the production of 131.4 and 132.8 g L-1 of ethanol (84.8% and 86.0% of theoretical yield), respectively, after 48 h fermentation. (C) 2014 Elsevier Ltd. All rights reserved.