The effect of prehydrolysis and improved mixing on high-solids batch simultaneous saccharification and fermentation of spruce to ethanol

► High solids SSF (13.7% water-insoluble solids (25% total solids)) was performed. ► The final ethanol yield in batch SSF was very low (5-6%). ► The liquid fraction of the steam-pretreated slurry did ferment well (85% yield). ► Improved stirring did not improve the final ethanol yield in high solids batch SSF. ► Prehydrolysis prior to high solids SSF increased the final ethanol yield to 72%.