COFCO Ltd, China's biggest grain trader and processor, will build a second plant in southern Guangxi Zhuang Autonomous Region to convert starch-rich cassava roots into ethanol, a company official said. The firm won a bid in January from the region's government to build the plant, which will add 300,000 metric tons of annual capacity to its existing plant of 200,000 tons a year, Lin Hailong, a research manager, said in Qingdao yesterday.