Corn stover is another potentially interesting feedstock for ethanol produc­tion, especially in the USA. The fermentation characteristics of S. cerevisiae RWB 218 on corn stover hydrolysate were tested under industrially relevant fed-batch conditions (W. de Laat, unpublished data). The corn stover pulp obtained after steam explosion (190 ° C, 5 min, ENEA, Italy) was diluted with water to 150gL-1 dry matter and subsequently hydrolysed with 10g cellu — lase protein (kg hydrolysate dry matter)-1 (GC220, Genencor, 96 h at 50 °C). After filtration, the resulting sugar solution contained 40 g L-1 glucose, 9 g L-1 D-xylose and 4 g L-1 acetic acid.

Fermentation experiments were initiated by a 32 h batch phase on mo­lasses medium (containing 100gL-1 sucrose, pH 4.8, 32°C) in a volume of 200 mL. Subsequently, 455 mL of corn stover hydrolysate was added during a 16 h fed-batch phase. During the fed-batch phase, glucose was almost com­pletely consumed. However, only 40% of the D-xylose fed to the culture was consumed during this phase (Fig. 9). After 16 h, the fed-batch phase was terminated and the culture was allowed to consume accumulated sugars. Con­version was complete after 35 h. At a biomass concentration of 1.0—1.5 gL-1, this corresponded to a D-xylose fermentation rate of 0.5 mmolg-1 h-1 dur­ing this latter phase. The overall ethanol yield on total sugars was 0.46 gg-1, which corresponds to 90% of the theoretical maximum yield on glucose and D-xylose. Consistent with the wheat straw hydrolysate fermentations, xylitol formation was not observed.

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