Christian Science Monitor: Somewhere between the exquisite vial of 25-year-old balsamic vinegar, fermented in cherry wood, that Modena’s Acetaia del Cristo sells for roughly $150 and the few dusty potatoes that Ann Petroni hawks on a blanket she brought with her from Burundi, lies the future of Slow Food, founded in 1989 to counteract the pernicious effects of fast food. Along with vinegar and potatoes, the accomplishments and contradictions of the organization were also on display last month at Terra Madre, a …