Previous simultaneous saccharification and fermentation (SSF) of switchgrass experiments using the thermotolerant IMB 3 strain of Kluyveromyces marxianus suggest that maintaining a pH at or slightly above 5.0 will result in increased ethanol production.  Switchgrass was pretreated with pressurized hot water at 200 ºC for 10 min.  Two 1.5 L SSFs will be performed in a stirred bioreactor.  The pH will be automatically controlled at 5.5 and 5.0 by adding 2 M potassium hydroxide and the temperature will be maintained at 45 ºC.  15 FPU/g glucan of cellulase enzyme will be used with a beginning glucan concentration of 40 g/L.  Samples will be taken every 24 hours for 7 days and analyzed by HPLC for ethanol, sugars, and organic acid concentrations.