Steam pretreatment of SO2 impregnated spruce chips
yields a material that is relatively easy to hydrolyze and
ferment, whereas dilute acid impregnation results in a
material harder to ferment because of the generation of
inhibitory compounds [12]. With present bench-scale technology,
it is possible to obtain around 300 litres of ethanol
per metric ton spruce, which is 70% of the theoretical
overall yield based on hexose sugars [12,13