A third Minnesota ethanol plant is considering a shift in production to a new biofuel called isobutanol.

Butamax Advanced Biofuels, a Wilmington, Del.-based joint venture that is competing to commercialize the technology, said Monday that it's signed up four more ethanol plants for potential retrofits to make the fuel. Others are in Iowa and Nebraska.

The latest plants in what Butamax calls its "early adopters group" are Granite Falls Energy of Granite Falls, Minn.; Platinum Ethanol of Arthur, Iowa, which is owned by Minnesota-based Fagen Inc.; Little Sioux Corn Processors of Marcus, Iowa, and Siouxland Ethanol of Jackson, Neb.

A plant in Luverne, Minn. owned by rival Gevo of Englewood, Colo., last month completed conversion to isobutanol production. Gevo plans other conversions but announced only one other, in Redfield, S.D.

Highwater Ethanol of Lamberton, Minn., announced in December that it might convert to the new fuel.

Butamax hasn't said which of its plants would be retrofitted first. The company, a joint venture of BP and DuPont, said it will break ground on one plant next year, complete it in 2014 and retrofit more based on demand.

Isobutanol, like ethanol, is an alcohol produced by fermentation of corn, though it uses genetically engineered yeast. The final product can be mixed with gasoline as a motor fuel or be used to make chemical products and plastics and is being tested as a jet fuel.

The announcement comes at a time of financial challenge and overcapacity in the ethanol industry. Five of six ethanol makers with plants in Minnesota that publicly report their financial results lost money in the most recent quarter, including Highwater Ethanol. The Granite Falls plant's profits fell, although it still made money.

One cloud over the new technology is that Gevo and Butamax are fighting over patents in U.S. District Court in Delaware. In six lawsuits, the companies have alleged patent infringement on genetically engineered yeast and plant technology.

A federal judge temporarily ordered Gevo to stop adding customers, a condition Gevo said isn't a problem for now because the Luverene plant's production is already sold.

All the plants announced Monday by Butamax were built by Fagen, a Granite Falls engineering and construction firm that has built many U.S. ethanol plants. Butamax recently announced a deal with Fagen to convert ethanol facilities for biobutanol production.

"Biobutanol is an exciting next step in the evolution of biofuels and presents a significant opportunity for companies such as ours to produce and market a higher-value product and reduce greenhouse gas emissions," Ron Fagen, owner of Platinum Ethanol LLC and Chairman of Fagen, said in a statement released by Butamax.

David Shaffer • 612-673-7090