Improving the fermentation characteristics of corn ( Zea mays L.) through agronomic and processing practices

Ethanol plants could improve their production efficiency if they processed grain best-suited for the fermentation process. This study determined the influence of hybrids, N fertility rates, harvest moisture levels, and drying temperatures on dry-mill ethanol production from corn produced in 2003 and 2004. Six hybrids ranging from 92 to 108 days in maturity were grown at Beresford and Brookings, SD, under four N fertilizer treatments: control (no N applied), 50% (one-half the recommended N rate for a typical yield goal), 100% (the recommended N rate for a typical yield goal), and 200% (double the recommended N rate for a typical yield goal). Ears from plots receiving the recommended N rate for a typical yield goal were hand-harvested at 25 and 20% grain moisture and were then dried to 15% moisture at the following temperatures in 2003: (1) room temperature (control), (2) 100°F, (3) 125°F, and (4) 140°F. The drying temperature treatments were increased in 2004 to: (1) 100°F, (2) 150°F, (3) 175°F, and (4) 200°F. Added N usually increased grain protein at the expense of starch. However, the 100% N rate for a typical yield goal did not adversely impact ethanol concentration. Three Processor PreferredRTM Highly Fermentable Corn (HFC) hybrids were grown at Beresford. One of the HFC hybrids yielded 0.4% more relative ethanol concentration than another HFC hybrid. This showed that the HFC ranking system may overestimate a hybrid's ethanol production potential in relation to other hybrids. The HFC rankings were not applicable at Brookings as none of the hybrids reached physiological maturity prior to the first autumn killing frost during both years. The Brookings site was useful in comparing the effects of maturity stage on ethanol production, as three of the hybrids reached physiological maturity prior to the first autumn killing frost at Beresford but not at Brookings. Relative ethanol concentration was reduced by 0.3% when grain had developed less than one-half of its hard starch layer prior to the first autumn killing frost. Relative ethanol concentration reductions of 0.1 to 0.4% typically occurred when corn was dried at 140°F in 2003 to 200°F in 2004 rather than at 100°F. Relative ethanol concentration generally did not differ between grain dried at 100 and 125°F in 2003. The room temperature (control) produced 0.1 to 0.3% less relative ethanol concentration than the 100 or 125°F drying temperatures when the grain was harvested at 25% moisture, but not when the grain was harvested at 20% moisture. Relative ethanol concentration was affected by the Hybrid x Drying Temperature interaction at Brookings, as increased drying temperatures did not impact ethanol production from the two most immature hybrids. These results suggest that farmers should apply the recommended N rates for their yield goals, plant hybrids that will mature prior to the first autumn killing frost, and dry corn between 100 and 125°F to prepare grain for optimum starch utilization for the ethanol industry. A multiple regression was implemented to predict ethanol concentration based the following variables from a non-destructive near infrared transmittance (NIT) grain analysis where starch, protein, oil, and extractable starch were measured. The NIT analysis produced a correlation coefficient of R2=0.37. The destructive Megazyme Total Starch Assay produced a correlation coefficient of R2= -0.0007.