Optimization of Fermentation Process Conditions in Ethanol Production from Sugarcane Molasses: The Case of Desta Alcohol and Liquor Factory

Abstract

Alcohol distillery processes are one of the agro based industries that produces different types of alcohol liquors to serve communities as a drink and raw material for other industries. Desta Alcohol and Liquor Factory (DALF) is one of Ethiopia's leading distillery alcohol producers, well-known for its iconic beverage brands. However, the company's alcohol fermentation process has significant inefficiencies and inconsistency in ethanol yield as realized by the existing process. Hence, this study aimed to optimize fermentation process conditions in line with systemic pretreatment of sugarcane molasses to reduce its ash content and calcium content. The experimental ethanol fermentation was carried out in four main stages, mainly sugarcane molasses pretreatment and characterization, yeast propagation, fermentation, and characterization of the fermented mash. The sugarcane molasses was pretreated using hot-acid pretreatment and characterized its physico-chemical properties followed the standard methods. After pretreatment, propagation of yeast in the treated molasses supplemented with DAP was carriedout in an incubator at 30 ℃ for 24 hours. The fermentation of sugarcane molasses was carriedout as per the RSM-CCD specified factors. In order to examine and optimize the effect of molasses concentration, inoculum size, pH, and temperature on fermentation process, 24 full factorial central composite design (CCD) was used using Design Expert® v.13 software. Pretreatment effectively reduced the ash and calcium content to 6.8% and 0.013%, respectively. The ANOVA analysis revealed that the ethanol yield was significantly impacted by the fermentation process factors and their interactions (p value < 0.05). As a result of the RSM optimization, the optimum ethanol yield of 10.958% (v/v) was found at 22.725 °Brix molasses concentration, 10.132% (v/v) inoculum size, 4.943 pH, and 32.82 ℃ temperature. For comparison, without pretreatment an ethanol yield of 9.37% (v/v) was found at the optimized fermentation conditions. The characteristics of the fermented molasses mash revealed that Brix of 9.67 °Brix, temperature of 32.5 ℃, specific gravity of 0.98, and pH of 4.93. The pretreated molasses and optimized process resulted in higher ethanol yield and distinct molasses mash characteristics. The rough design and techno-economic analysis shows that hot-acid pretreatment is both technically feasible and financially viable, supporting its implementation at DALF.