This study investigated the application of dark fermentation to obtain value-added soluble metabolite products (SMP) from vinasse as a strategy to enhance the energy efficiency in sugarcane biorefineries. Batch tests comparing sucrose and vinasse as the substrates were conducted, providing data to both understand conversion pathways and measure the energetic implications of fermenting vinasse under controlled conditions. Two distinct inoculum pretreatment methods, namely, acid-thermal and thermal were also assessed. Overall, butyrate fermentation was the primary conversion pathway observed in vinasse acidogenesis, leading to butyric/isobutyric acid concentrations over 6.0 g L-1, irrespective of the inoculum pretreatment. Lactic and malic acids were the primary substrates, with the predominance of the lactate-to-butyrate fermentation, suggesting the establishment of a syntrophic relation between lactate-producing bacteria and clostridial populations. Considering energetic aspects, the enhanced butyrate production could lead to an energy recovery potential of 30.9-33.4 MW, outcompeting highly-efficient biohydrogen- (<1.0 MW) and methane-producing (25.5 MW) anaerobic systems, in order to increase sugar conversion efficiency by 7.8%. Although important technological aspects still require proper attention to cost-efficiently scale-up SMP recovery from fermented substrates, the energetic relevance of butyrate production from vinasse was proved, characterizing an efficient approach to enhance the energy performance of sugarcane biorefineries. (C) 2020 Elsevier Ltd. All rights reserved.