Direct fermentation of unhydrolyzed potato starch to ethanol by monocultures of an amylolytic fungus,
Aspergilus niger, and cocultures of A. niger and Saccharomyces cerevisiae was investigated. Amylolytic activity,
rate and amount of starch utilization, and ethanol yields increased several-fold in coculture versus the
monoculture due to the synergistic metabolic interactions between the species. Optimal ethanol yields were
obtained in the pH range 5 to 6 and amylolytic activity was obtained in the pH range 5 to 8. Ethanol yields were
maximal when fermentations were conducted anaerobically. Increasing S. cerevisiae inoculum in the coculture
from 4 to 12% gave a dramatic increase in the rate of ethanol production, and ethanol yields of >96% of the
theoretical maximum were obtained within 2 days of fermentation. These results indicate that simultaneous
fermentation of starch to ethanol can be conducted efficiently by using cocultures of the amylolytic fungus A.
niger and a nonamylolytic sugar fermenter, S. cerevisiae.