Development of an ethanol yield procedure for dry-grind corn processing

In 2008, the United States produced ethanol at a rate of 39.5 billion L/year; an additional 8.5 billion L/year capacity was under construction. Kernel composition and physical properties are not correlated with ethanol yield. A procedure that measured the potential of hybrids to produce ethanol would benefit corn seed companies, corn producers, and ethanol processors. The objective was to develop a laboratory procedure to measure ethanol yield from corn samples and evaluate the developed procedure for accuracy and precision. To determine parameters for routine analyses, effects of mill type, dry solids, and yeast addition were investigated separately followed by effects of fermentation time (Tf), glucoamylase dose, and yeast addition. Measurement of ethanol using HPLC and gravimetric (change in weight due to CO₂ loss) methods were compared. Using the procedure developed, ethanol yields for five diverse hybrids (dent, waxy, white, high oil, and high amylose) were measured. Effects of mill type, dry solids, Tf, glucoamylase dose, and yeast addition were significant (P < 0.05). The gravimetric method estimated higher yields (428 ± 10 L/tonne) than HPLC (405 ± 15 L/tonne) and had a higher level of precision. Both methods had coefficients of variations of <4% and gave similar conclusions. In the final procedure, we used corn (25 g/batch) liquefied with α-amylase (60 min at 90°C) in 75 mL of distilled water. Simultaneous saccharification and fermentation was used (64 hr at 32°C) with glucoamylase and yeast. Gravimetric and HPLC methods measured differences in ethanol yield for the five hybrids (158-435 L/tonne). The method is suitable for routine testing of ethanol yield potential and as a reference method for verifying more rapid measurement techniques.