(89d) Low Cost Medium for Starch Particle Fermentation

The direct conversion of starch particles to ethanol was developed using barley α-amylase to produce glucose and Saccharomyces cerevisiae as the fermentation microorganism. This technology removes the need to cook starch and thus reduces energy costs for the bioethanol industry, so is now used commercially in the USA. However, one serious drawback is the requirement to include high quantities of expensive enzymes to break down the insoluble starch particles. A low cost medium has been developed in this work and shown to produce superior yields of ethanol, 0.51 g ethanol / g starch, compared to expensive medium, 0.46 g ethanol / g starch. The new medium reduces the simultaneous hydrolysis and fermentation medium costs by 80% compared to expensive medium and requires no addition of costly enzymes. In continuous bioreactor runs using the inexpensive medium, steady state conversions of starch to ethanol were achieved at dilution rates up to 0.25 h^-1 with complete utilization of the starch and high yields of ethanol.