Eight trace elements were screened for increasing efficiency of ethanol yield from sweet sorghum juice using the Plackett-Burman design method. MnCl2 center dot 4H(2)O, CoCl2 center dot 6H(2)O and biotin was screened as the significant variables which have positive effects on ethanol production from sweet sorghum juice. The values of MnCl2 center dot 4H(2)O, CoCl2 center dot 6H(2)O and biotin, optimized by Box-Behnken design method, were 7.70 mg L (1), 15.74 mg L (1) and 11.97 mg L-1, respectively. The experimental efficiency of ethanol yield under optimal conditions was 89.30 +/- 0.10%, which enhances the efficiency of ethanol yield by 5.63% by the addition of MnCl2 center dot 4H(2)O, CoCl2 center dot 6H(2)O and biotin. The results from this study have identified optimal conditions as a foundation for pilot scale ethanol production. (C) 2012 Elsevier Ltd. All rights reserved.