Abstract: The invention relates to a process and system for the production of a solvent using monophasic solventogenic Clostridia in a single stage process. More particularly, the process and system relate to the use of a culture vessel for culturing monophasic solventogenic Clostridia, wherein cell growth of the Clostridium is monitored and optimized by the addition of controlled amounts of culture media and/or the removal of controlled amounts of solvent. The process and system may particularly be used to produce solvents such as butanol, acetone and ethanol.