The president of the National Corn Growers Association says a more efficient type of ethanol is the future of liquid fuel, even though it’s a few years away.Ron Litterer was part of an energy panel at the Louisville Forum Wednesday. In his comments, he mentioned the increased efficiency of cellulosic ethanol, which uses more of the corn plant to produce fuel.Afterwards, Litterer said developing the technology is essential to ethanol’s continued use.“Certainly the next step is going to be the cellulosic part which the corn plant itself can contribute to with the cob and part of the stalk," he said. "That’s going to be an evolution that’s going to happen over a number of years but it is going to improve the efficiency of corn-based ethanol.”Litterer said once cellulosic ethanol becomes standard, current plants could be retrofitted to produce the fuel.