Burien, Wash.—The recent pledge by the Federal Reserve to keep interest rates low until 2013 may be good news for borrowers, but potential new investors in the wine business continue to encounter financial barriers.A telling example of the challenges facing would-be vintners surfaced earlier this year, when Sherrill Miller began selling E.B. Foote Winery in pieces: Prospective buyers were unable to secure the financing needed to acquire the successful business.