Enhancement of ethanol production by promoting surface contact between starch granules and arming yeast in direct ethanol fermentation.

The specific ethanol production rate of raw starch by arming yeast cells displaying alpha-amylase and glucoamylase increased significantly when the cells and starch granules settled together. The specific ethanol production rate also increased when the size distribution of starch granules was almost same as that of the yeast cells. These results indicate that the surface contact between starch granules and yeast cells is important for increasing the apparent specific activity of alpha-amylase, which was the rate-limiting factor of the direct fermentation.