An unusual and versatile alternative to vinegar, verjuice--or verjus--is the golden juice of unripened green grapes. Delicate, sweet-tart, and clear, verjuice was very popular in the Middle Ages until it was eclipsed by the lemon, which was brought back to France from the Crusades. Because it shares the same acid base as wine, verjuice will not distort the essence of wine, the way a vinegar-based dressing may. Like lemon juice, verjuice heightens the flavors of soups and sauces, makes an excellent marinade, and may be used for cooking or deglazing. It's soft and flavorful enough to use all by itself as a salad dressing. In summer, mixed with water or straight, it makes a refreshing and unusual beverage with much less sugar than other fruit juices. Refrigerate after opening.