text: The process may be likened to how yeast ferments sugars to produce ethanol for wine, beer, or fuel, but the organisms that carry out the ABE fermentation are strictly anaerobic (obligate anaerobes). The ABE fermentation produces solvents in a ratio of 3 parts acetone, 6 parts butanol to 1 part ethanol. It usually uses a strain of bacteria from the Class Clostridia (Family Clostridiaceae). Clostridium acetobutylicum is the most well-studied and widely used. Although less effective, Clostridium beijerinckii and Clostridium saccharobutylicum bacterial strains have shown good results as well.
  The ABE fermentation pathway generally proceeds in two phases. In the initial acidogenesis phase, the cells grow exponentially and accumulate acetate and butyrate. The low pH along with other factors then trigger a metabolic shift to the solventogenesis phase, in which acetate and butyrate are used to produce the solvents.
  For gas stripping, the most common gases used are the off-gases from the fermentation itself, a mixture of carbon dioxide and hydrogen gas.