WASHINGTON — What’s sweet like sugarcane, looks something like corn and could be grown in much of the United States to make ethanol? Sweet sorghum.
American pioneers used sweet sorghum as a substitute for sugar to make syrup. The syrup still is available today, mostly made in Kentucky and Tennessee, but for decades, most American sweet sorghum has been used for livestock feed. Today, some researchers are looking at using it to make ethanol to blend with gasoline and help reduce the country’s dependence on oil.
The timing may be right for sweet sorghum. The United States is reaching its limits on using corn for ethanol, and global concerns are rising about using grains to make fuel while food prices soar.
At the same time, researchers are looking for ways to make biofuels that would do more to reduce carbon-dioxide emissions. Sweet sorghum gets good marks on all counts.
In India, where researchers made ethanol from sweet sorghum recently, it’s known as a smart crop because farmers can grow it for grain for food or for the stalks for animal feed or ethanol. It will grow in hot and dry conditions, and it tolerates salty land and waterlogging.
Sweet sorghum is harvested for its juice before the mature plant forms clusters of grain. The stalks are pressed, and the juice is fermented and distilled to make ethanol. The process is simpler and requires less electricity than making ethanol from corn.
Growing sweet sorghum requires only about half the water needed for corn and about half the nitrogen fertilizer. And unlike sugarcane, which grows best in tropical conditions, fast-growing sweet sorghum can be grown in much of the country during the summer.
But the crop has a big drawback: It’s bulky to transport and can’t be stored. In fact, processing has to start within about 24 hours after harvesting or sugar will be lost.
Researchers are looking for better breeds of sweet sorghum and small-scale processing systems that might make economic sense.
“Sweet sorghum is really the sugarcane of the Middle West,” said Michael McNeill, who runs an agricultural consulting business in Algona, Iowa.
Studies at U.S. universities have shown that an acre of sweet sorghum could yield enough juice for 400 to 600 gallons of ethanol, compared with 434 gallons from an acre of corn.
“It’s pretty simple. It’s low-energy input,” said Danielle Bellmer, an associate professor of biosystems engineering at Oklahoma State University. “I just think it makes a whole lot of sense.”
Sweet sorghum in the Midwest is harvested in September and October — after nights get cool but before a hard frost. That means there’s only about a two-month harvest period when ethanol plants could run.
The crop would have a longer window in the South but still couldn’t be grown from October to March.
Robert Anex of the department of agricultural and biosystems engineering at Iowa State University said it would be difficult to make an ethanol plant pay for itself if it ran for only a few months each year.
He figures it would be “exceedingly difficult” to make a viable business out of sweet-sorghum ethanol in North America, especially in the Northern Plains states.
