Vinters in Modena, Italy have been making balsamic vinegar for nearly 1000 years and the process is similar to that of making wine. Sweet, white Trebbiano grape pressings (called “must”) are simmered for hours and hours until they have become thick and caramelized. The resulting syrup is then aged in a succession of barrels made from different kinds of wood that give the vinegar character. Authentic balsamic vinegar is aged no less than 12 years.
White balsamic vinegar, however, blends white grape must with white wine vinegar and is cooked at a low temperature to avoid any darkening.