The course of fermentation of thick juice as intermediate product of sugar beet processing by yeast Saccharomyces cerevisiae was studied in the paper. The feasibility of ethanol production from thick juice was experimentally confirmed in batch fermentation in a bioreactor of 1.5 L working volume. Important parameters for modelling of the process using response surface methodology were defined by analyzing the results of the course of fermentation. For description of the response function of the number of yeast cell number, ethanol volume fraction and total sugar mass fraction during fermentation, the effects of initial sugar content in the range 5-25% w/v and duration of fermentation in the range 0-48 h, were examined. Obtained models have contributed to a better understanding of the impact of different initial sugar mass fractions, fermentation time and interactions of these factors on the selected responses. Optimization of multiple responses was also simultaneously performed i.e. maximization of both yeast cell number and ethanol volume fraction while residual total sugar mass fraction was minimized. Results of optimization suggest that the optimal conditions are fermentation time of 46 h and initial sugar mass fraction of 20.67%. Further research was performed to validate the obtained results and confirm their applicability in the enlarged scale. The results obtained during the fermentation in bioreactor of 10 L working volume under optimal conditions defined for fermentation in the bioreactor of 1.5 L working volume were in good correlation. (C) 2011 Elsevier Ltd. All rights reserved.