Detrimental effect of increasing sugar concentrations on ethanol production from maize or decorticated sorghum mashes fermented with Saccharomyces cerevisiae or Zymomonas mobilis: Biofuels and environmental biotechnology

The efficiency of ethanol fermentation, as affected by grain source (maize and decorticated red sorghum), total sugar concentration (13 or 20° Plato) and type of microorganism ( Saccharomyces cerevisiae or Zymomonas mobilis ) was studied. Maize mashes yielded 0.32 l ethanol kg −1 ground grain whereas mashes prepared with decorticated red sorghum produced 0.28 l ethanol kg −1 . Both microorganisms yielded similar amounts of ethanol. However, high-gravity mashes (20° Plato) yielded lower amounts of ethanol compared to counterparts adjusted to 13° Plato (0.28 vs. 0.22 l ethanol kg −1 ground grains). In decorticated sorghum mashes adjusted to 20° P, Z. mobilis produced 40 ml kg −1 more ethanol compared to S. cerevisiae. In addition , Z. mobilis had a lower dependency on nitrogenous compounds.