Factors Adversely Affecting Ethanol Production in the Dry Grind Processing of Sorghum

Abstract

Many factors may contribute to the low ethanol yield and fermentation efficiency of sorghum varieties. The effects of particle size of ground sample, viscosity, enzyme-resistant starches, and protein matrix on ethanol fermentation have been investigated. Finely ground samples could yield as much as 5% more ethanol than coarsely ground samples. Samples with a dense protein matrix around starch granules had low ethanol yield and fermentation efficiency; steeping with sodium bisulfate or treating with protease both improved ethanol fermentation efficiency by up to 2.5-3.0%. The significantly reduced residual starch content in the DDG of the treated samples further confirmed the effects of steeping and protease treatment. A starch-rich fraction that escaped enzyme hydrolysis during mashing was separated from the mashed residues of a low efficient sample. The amount of this fraction accounted for approximately 2.5% of the total starch. DSC thermogram showed three distinct endothermic peaks at 98 °C, 110 °C, and 142 °C. More studies to characterize the chemical and physical properties of this fraction are in progress. The fermentation efficiency of low-ethanol yielding sorghums could reach levels comparable to those of corn when appropriate integrated strategies are applied.