Influence of temperature, pH and yeast on in-field production of ethanol from unsterilized sweet sorghum juice

Abstract

It is inevitable that ethanol production in the United States will continue to increase. Sweet sorghum has the potential to be used as a renewable energy crop, and is a viable candidate for ethanol production. Previous barriers to commercialization of sweet sorghum to ethanol have primarily been the high capital cost involved in building a central processing plant that may be operated only seasonally. In order to reduce the investment necessary in a central processing facility, the proposed process involves in-field production of ethanol from sweet sorghum. The overall objective of the research was to determine whether fermentation can take place in the environment with no process control. The goals were to evaluate the effects of yeast type, pH, and nutrients on fermentation process efficiency. Results indicated that both strains of Saccharomyces cerevisiae tested were able to perform fermentation within a wide ambient temperature range (10–25 °C). Maximum ethanol produced was 7.9% w v−1 in 120 h under ambient temperature conditions. Other process variables such as adding urea or lowering pH did not significantly improve the sugar to ethanol conversion efficiency of yeasts. Results indicate that in-field fermentation of sweet sorghum juice to ethanol is possible with minimal or no process controls and is a feasible process for ethanol production.