Combine all ingredients except peppercorns and wine in a 4 litre pot. Pour over just enough water to cover and heat on high heat until liquid comes to a boil. Turn heat down, cover pot and keep broth at a slow simmer. When vegetables have simmered 30 minutes, add peppercorns and white wine and simmer for 10 minutes more. Strain through a medium-mesh strainer into a clean pot or heat-resistant plastic container. Let broth cool, uncovered, for an hour before putting it in the refrigerator.