9.3.1 Microorganisms and Their Characteristics

Microorganisms are a key component of the technology used in different fermen­tation regimes, including ethanol. Diverse groups of microorganisms are capable of producing ethanol. These include yeasts, Saccharomyces cerevisiae, Schizosac — charomyces pombe, bacteria Zymomonas mobilis, fungus Fusarium oxysporum, yeast-like fungus Pachysolen tannophylus, and thermophilic bacteria [28]. Saccharomyces cerevisae and Schizosaccharomyces pombe represent the organism of choice for the industrial production of ethanol due to the following features:

• Capable of fermenting a diverse range of sugars and sole production of ethanol, CO2 under anaerobic conditions

• Due to their comparatively bigger size, they flocculate well to supply clean wash to the still and the wash and distillate lack offensive odor

• Contamination problem is under control as the fermentation process operates at low pH and high sugar concentration

• Are genetically stable and ferment 20-25% (w/v) sugar in molasses solution completely