Ethanol fermentation of HTST extruded rye grain by bacteria and yeasts

Abstract

AbstractHigh temperature extrusion cooking of rye was used as a pretreatment for ethanol fermentation, and yeasts and bacteria were compared for their fermentation rates. Extrusion cooking caused, on average, a 7.5% increase in ethanol yield in comparison to autoclaved samples. The best results were achieved for grain with a moisture of 21‐23% which was extruded at temperatures of 160‐180 °C.Extrusion decreased the relative viscosity of rye grain water extracts, so it was possible to mash it without α‐amylase. The efficiency of fermentation of extruded rye without Termamyl was equal to that of autoclaved and traditionally mashed rye (using α‐amylase).The rate of fermentation of extruded rye grain by Zymomonas was higher during the first stage, but the final ethanol yield was similar for the bacterium and the yeast.Though both microorganisms gave good quality distillates, the concentration of compounds other than ethanol achieved from extruded rye mashes, which were fermented by Z. mobilis, was five times lower than for yeasts.