Why do recipes for raisin pie specify vinegar?
A. Sometimes raisin pie recipes call for lemon juice instead of the vinegar and sometimes tart fruits like apples, oranges and cranberries are combined with the raisins. All of these acid ingredients have just one real function flavor. Raisins tend to be very sweet and adding sugar and cooking them makes them even sweeter. The little bit of acetic, ascorbic or citric acid from the vinegar or the fruits offsets that sweetness, enhances the raisin flavor, and gives an impression of added freshness. One other side benefit from these acid ingredients is that they keep the starch gel softer and thereby keep the pie fresher for longer.
