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Title: Effects of ground corn particle size on ethanol yield and thin stillage soluble solids

item Johnston, David

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2006
Publication Date: 7/1/2006
Citation: Naidu, K., Singh, V., Johnston, D., Rausch, K.D., Tumbleson, M.E. 2006.Effects of ground corn particle size on ethanol yield and thin stillage soluble solids. Cereal Chemistry, Vol. 84, No. 1, p.6-9.

Interpretive Summary: The rapid growth of the fuel ethanol industry and the concomitant increase in distillers dried grains with solubles (DDGS, a dry animal feed coproduct) is necessitating improvements and optimization of the overall process. The first step and a very significant aspect of the fuel ethanol process is the grinding of the whole corn kernels. The size distribution of the ground particles could have significant effects on multiple aspects of the overall process. In order to address these interactions, corn was ground to different particle sizes and then evaluated using a laboratory scale process. The results clearly show that there are significant differences in ethanol yields depending on the ground corn particle size used and the smaller particles increase the final ethanol yields. The results also show that the smaller corn particles increase the amount of soluble solids in the liquid after the ethanol is removed. A soluble solids level that is too high can negatively affect the DDGS recovery process. These results will be useful to other ethanol researchers and producers and could help contribute to lowering the production cost of fuel ethanol benefiting farmers and fuel ethanol consumers.

Technical Abstract: The effects of ground corn particle size on ethanol yield and soluble solids in thin stillage were evaluated using a 2-L laboratory dry-grind procedure. The procedure was optimized for grinding, liquefaction, saccharification, and fermentation parameters. The optimized procedure was reproducible with a coefficient of variation of 3.6% in ethanol yield. Five particle size distributions of ground corn were obtained using a crossbeater mill equipped with five screens (0.5, 2, 3, 4, and 5 mm). Particle size had an effect on ethanol yield and on soluble solids concentration in thin stillage. The highest ethanol yield of 12.6 mL/100 mL of beer was achieved using a 0.5-mm screen in the cross-beater mill. Treatment using the 0.5-mm mill screen resulted in soluble solids concentration of 25.1 g/L and was higher than soluble solids concentrations obtained with other screens. No differences in soluble solid concentrations were observed in samples of thin stillage obtained from 2, 3, 4, and 5-mm screens which had a mean yield of 16.2 g/L. By optimizing particle size for maximum ethanol yield and minimum solids in thin stillage, dry-grind corn plants could realize reduced capital and operating costs.