FEW: Stargen for noncook sorghum applications

By Jessica Sobolik | June 02, 2008
Web exclusive posted June 18, 2008 at 6:08 p.m. CST

More than three years ago, Genencor Inc.—now a Danisco company—released its new trademarked Stargen enzyme for raw starch hydrolysis applications in corn-based ethanol plants. Raw starch hydrolysis allows plants to skip the cooking step, saving them time and energy. Recently, the company conducted research on these same enzymes to be used in noncook applications in sorghum-based ethanol plants. Gang Duan, a company director, presented Genencor's findings in a breakout session focusing on enzyme technology at the 2008 International Fuel Ethanol Workshop & Expo in Nashville, Tenn., on June 18.

Duan first acknowledged the fact that sorghum isn't a widely used ethanol feedstock. He said approximately 5 percent of U.S. ethanol is made from the grain at eight different ethanol plants, and it's mostly used in tandem with corn in the south-central part of the United States. However, he pointed out that sorghum is more price competitive than corn in certain areas. It also requires less water than the corn-based production process. Furthermore, distillers grains from sorghum are of equal value to distillers grains from corn.

When cooking corn in the ethanol production process, the slurry needs to be heated to approximately 100 degrees Celsius. Sorghum must be heated to approximately 130 degrees. For that reason, producers should consider a noncook system that would simply bypass the jet cooker, liquefaction and saccharification processes, Duan said. The noncook system could bring sorghum fermentation efficiency to 95 percent, versus less than 90 percent using a cooking method. Less cooking means less unit operation, and less energy consumed to heat and cool the slurry. Furthermore, components of sorghum that are difficult to break down after using a cooking method, such as tannins and protein, are easier to break down if not cooked. "When sorghum is heated up, it reacts with amino acids or protein, and forms chemicals that may be interesting … but not to ethanol producers," Duan said.

When it comes to the resulting distillers grains, protein digestibility is improved. The phytic acid and free phosphate contents are lower. Phosphate disposal, which is an environmental concern, is thus reduced. By installing a noncook system, new facilities don't spend as much in capital investments, and construction is completed more quickly. Duan said the system could easily be adopted in existing facilities by simply installing equipment that bypasses the cook steps.

"Hopefully after my talk, you feel a little more comfortable using sorghum," Duan concluded.