Evaluation of bioethanol production from five different varieties of sweet and forage sorghums (Sorghum bicolor (L) Moench)

Cultivars of sweet (Rio, M81E and Della) and forage sorghums (Tato and Thor) were planted in Northeast Mexico in order to estimate optimum harvesting time, sugar production, biomass composition and ethanol yields. The juices were characterized in terms of sugar composition, free amino nitrogen (FAN) and phenolics and then yeast (Saccharomyces cerevisiae)-fermented into ethanol. The cultivars yielded different volumes of sweet juice and total sugars. They also had different optimum harvesting times. Glucose was the most abundant sugar in raw juices, followed by fructose and sucrose. FAN concentration ranged from 19 to 36 mg L⁻¹ therefore, nitrogen supplementation was required for adequate fermentation. After 18 h fermentation, there were no differences in efficiencies among cultivars but the sweet sorghums yielded more ethanol Ha⁻¹ compared to the two forage sorghums (approximately 1000 L Ha⁻¹ versus 770 L Ha⁻¹). Della was the cultivar with the highest productivity with 1051 L Ha⁻¹ ethanol produced after the first cut.