| abstract |
Starch is converted to ethanol by a process in which an aqueous starch slurry is hydrolyzed in sequential liquefication and saccharification steps to provide sterile saccharified starch solution containing from about 60 to about 80 weight percent of fermentable sugar based on the weight of the original starch present and the fermentable sugar is thereafter continuously converted by fermentation to dilute aqueous ethanol ("beer") in a series of agitated fermentation vessels which contain progressively more ethanol and less fermentable sugar employing at least two strains of yeast for the fermentation, one of which provides a high rate of ethanol production in a fermentation medium containing a relatively low concentration of ethanol and a relatively high concentration of fermentable sugar and the other of which provides a high rate of ethanol production in a fermentation medium containing a relatively high concentration of ethanol and a relatively low concentration of fermentable sugar. |