Fermentation pH, incubation temperature, and presence or absence of media buffer can alter the activity of microorganisms. For instance, carbon monoxide and hydrogen components of syngas show decreased solubility with increasing temperature. Clostridium species preferentially switch from acetogenesis to solventogenesis phase at pH below 5.0, and morpholinoethanesulfonic acid (MES) added as media buffer has been shown to increase lag time for ethanol production. The objective of the present study was to determine the effects of temperature, pH and MES buffer on ethanol production by "Clostridium ragsdalei". This study showed syngas fermentation using "Clostridium ragsdalei" at 32 degrees C with media without buffer was associated with higher ethanol concentration and reduced lag time in switching to solventogenesis. Temperature above 40 degrees C and pH below 5.0 were outside the optimal range for growth and metabolism of the bacteria. (C) 2011 Elsevier Ltd. All rights reserved.