In Italy, true balsamic vinegar is not considered an acidic ingredient for salad dressings, but rather a condiment to sprinkle on grilled meats or the best strawberries of the season. There are three very different kinds available: aceto balsamico tradizionale, commercial, and condiment.
Aceto balsamico tradizionale, or “traditional balsamic vinegar,” is made in small quantities under rigorously controlled conditions in and around the towns of Modena and Reggio Emilia in Emilia-Romagna. This artisanal product is protected by Italian law and by the European Union’s designation of original standards. Created from the boiled-down juice of sweet white grapes (traditionally Trebbiano), it has an underlying sweetness and takes on additional complex flavors from sequential aging in chestnut, oak, and other wood barrels. The long aging further evaporates the liquid, giving it a slightly viscous body. The name comes from balsanum, Latin for an aromatic resin that soothes and relaxes (the English balm is from the same word), indicating that the condiment was originally considered healthful and even used as medicine. Tradizionale must age for 12 year, so it is always expensive, but worth every penny.
Mass-market commercial balsamic vinegar, which is made from artificially flavored red wine and is not aged, is sometimes labeled “balsamic vinegar of Modena.” To improve its flavor and body, add a large pinch of brown sugar for every cup of vinegar.
Condimento balsamic vinegar is often good, and can be a fine alternative to commercial balsamic of questionable quality and the excellent but expensive tradizionale. It is usually made in Modena or Reggio Emilia, and often follows many of the same traditional manufacturing methods as its pricey relative. But unlike aceto balsamico tradizionale, condiment is not protected by a determined set of standards, so big differences can exist among brands. When you find one you like, stick with it.
Many chefs use a drizzle of boiled-down balsamic vinegar to decorate plates and act as an additional flavoring element. To make this useful garnish, boil 1 cup commercial balsamic vinegar in a nonreactive saucepan over a high heat until it has reduced by about three-fourths and is thickened and syrupy. It will keep indefinitely stored in a tightly closed jar at room temperature.