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Ethanol Production - Dry versus Wet Grind Processing

Traditionally, ethanol from corn has primarily been produced through dry- and wet-milling processes. The majority of U.S. ethanol production is from dry-grind technology. The traditional dry-grind process grinds the whole corn kernel and mixes it with water and enzymes. The mash is then cooked to liquefy the starch further. The mash is then cooled and mixed with more enzymes to convert the remaining sugar polymers to glucose before fermenting to ethanol (Murthy, et al., 2006). The components of the kernel not fermented include the germ, fiber, and protein, and are concentrated in the distillers dried grains that are produced as co-products. While dry milling is less capital intensive, it also yields less ethanol per bushel of corn than wet milling (Rajagopalan, et al., 2005).

Wet milling involves steeping the corn for up to 48 hours to assist in separating the parts of the corn kernel. Processing the slurry separates the germ from the rest of the kernel, which is processed further to separate the fiber, starch, and gluten. The fiber and corn gluten become components of animal feed while the starch is fermented to become ethanol, corn starch, or corn syrup (Renewable Fuels Association, 2005).

References

Murthy, G. S., V. Singh, D. B. Johnston, K. D. Rausch, and M. E. Tumbleson. 2006. "Evaluation and Strategies to Improve Fermentation Characteristics of Modified Dry-Grind Crop Processes." Cereal Chemistry, 83(3):435-459.

Rajagopalan, S., E. Ponnampalam, D. McCalla, and M. Stowers. 2005. "Enhancing Profitability of Dry Mill Ethanol Plants." Applied Biochemistry and Biotechnology, 120(1):37-50.

Renewable Fuels Association. “How Ethanol is Made.” 2005b. Retrieved February 2008.

Contributors

Cole Gustafson, North Dakota State University
Jason Fewell, Kansas State University

NDSU, Dept. 7620

P.O. Box 6050

Fargo, ND  58108-6050

Phone: 701.231.7261

Fax: 701.231.1008

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