Dear Stan: Great question. Raisins actually can ferment on their own. In fact, sun-dried raisins in particular have many more yeasts and microbes clinging to them than fresh grapes. In antiquity, wine was probably made by soaking sun-dried raisins in a bit of water and allowing the yeasts on the raisins to convert the sugar in the raisins to alcohol. Most store-bought raisins are coated with a bit of oil to help prevent them from sticking. That coating effectively blocks fermentation.