SAN FRANCISCO — Stone-Buhr Flour, a 100-year-old brand based in San Francisco, has launched an initiative called that allows consumers to trace their bag of flour back to the farm where the wheat was grown and harvested. By typing in the product’s "lot code" on the bag into the web site consumers are directed to a map that shows the farm where the wheat was grown and provides a forum for consumers to ask questions directly of the farmers. Josh Dorf, chief executive officer of Stone-Buhr who acquired the brand in 2001 from Unilever, said the idea behind the initiative was to create an identity-preserved certified-sustainable brand of flour that is good for the environment and local farming communities. Wheat for the brand’s flour comes from 32 farmers in the Pacific Northwest and is milled at a Spokane, Wash., facility.