Solid State Ethanol Fermentation of Apple Pomace as Affected by Moisture and Bioreactor Mixing Speed

Abstract

Solid state ethanol fermentation was conducted on apple pomace in a 40 L capacity horizontal batch reactor at 30°C using apple pomace moisture contents of 77 and 85% wb, mixing speeds of 2, 20 and 40 rpm and Saccharomyces cerevisiae ATCC 24702. A higher mean maximum ethanol concentration of 19.26% db was obtained at 85% wb moisture, whereas a mean ethanol of 18.10% db was produced at 77% wb pomace moisture. Mean ethanol concentrations during fermentation of 10.79 and 10.27% db, at bioreactor mixing speeds of 2 and 20 rpm, respectively, were significantly higher than the corresponding value of 9.30% db obtained at 40 rpm mixing speed. Maximum ethanol concentrations were attained earlier at 2 and 20 rpm than at 40 rpm. A linear regression model for fermentation efficiency was fitted as a function of initial glucose and moisture.