A sugary sap inside the plant's stalk, which grow as tall as 12 feet, can be turned into a potent biofuel, and experts and companies are studying its potential with hopes that farmers will want to plant more of it.
Ethanol made from the stalk's juice has four times the energy yield of the corn-based ethanol, which is already in the marketplace unlike sweet sorghum. Sweet sorghum produces about eight units of energy for every unit of energy used in its production. That's about the same as sugarcane but four times as much as corn.
"I think it can be a piece of the puzzle" as a biofuel crop, said Danielle Bellmer, executive secretary of the Sweet Sorghum Ethanol Association and an Oklahoma State University researcher studying ways to improve stalk pressing and fermentation methods. "The real issue is it's just not a well-known crop."
Currently about 10 million tons of grain from the tops of the plant's stalks are harvested in the U.S., the world's leading grower, but most of the sugar from the stalks goes to make syrup that people use to pour on biscuits, cook, and feed animals.
One company, Global Renewable Energy LLC, hopes to change that. It has planted two 20-acre plots to conduct tests with an eye toward using the plant for ethanol production.
"The purpose of those are obviously the testing, but we want to bring farmers and investors out," said Ray Coniglio, a spokesman for the Sebastian, Fla.-based company.
Sweet sorghum growers in South Texas and South Florida can get two crops a year because of their tropic-like weather. The crop, though, can be grown as far north as Canada. It grows in dry conditions and tolerates heat well.
In Texas and Florida, the second crop doesn't need to be planted; it sprouts from the first harvest. "We've found the contents are as good as the first crop," Coniglio said.
Sweet sorghum also spares the environment. Less fertilizer is needed than with corn and as a result there is less water contamination, Coniglio said.
Sweet sorghum differs from grain sorghum, which is grown on about 100 million acres worldwide. Sweet sorghum could be grown on about half of those.
"I think it will add more ethanol to the market," said Morris Bitzer, the executive secretary of the National Sweet Sorghum Producers and Processors Association, which has 500 members in 38 states.
The crop has caught the attention of the U.S. Agriculture Department, which along with Texas A&M University is sponsoring a conference on its use as a biofuel in Houston in August.
"I'm excited that they recognize that there are more feedstocks than just corn and switchgrass," Oklahoma State's Bellmer said.
In developing countries across Africa and in India, the grain is also used as food — to make a porridge and a flat bread — though its taste is rather bland, experts said.
Sweet sorghum in those countries that's turned into ethanol is allowing money that used to go overseas to buy oil to remain in rural economies.