Issues with In-Field Fermentation of Sweet Sorghum Juice

Abstract

Sweet sorghum has the potential to be used as a renewable energy crop, and has become a viable candidate for ethanol production. Advantageous properties of this crop are that it is a low input, high carbohydrate producer, and can be cultivated in nearly all temperate climates. In order to reduce the high capital investment necessary in a central processing facility, the proposed process involves in-field production of ethanol from sweet sorghum, where the juice would be pressed, collected, stored, and fermented in the field. In order for fermentation to take place in environmental conditions, several critical issues need to be addressed. Sweet sorghum juice was pressed using a triple-roll press and fermented under various conditions. The effect of delayed yeast inoculation was tested, with inoculation time ranging from 4 hours to 36 hours after pressing. The effect of time of harvest and the effect of stripping leaves and heads from the stalks before pressing on fermentation efficiency were investigated. Results showed that delayed inoculation resulted in significant decreases in ethanol yield, with nearly a complete loss after about 36 hours. The effect of time of harvest on fermentation efficiency was minimal, but the effect of leaf stripping showed significant improvement in fermentation efficiency. These results will help in optimization of the in-field fermentation process that may make sweet sorghum ethanol a reality.