While vinegar is "wine turned sour", real Balsamico is something else altogether. What you might commonly find in supermarkets are commercial products proclaiming to be balsamic vinegar, but most are pale representations and only vaguely akin to traditional Balsamico.
The unique and traditional Balsamic vinegar of Modena, Italy is made from the fresh "must" (unfermented juice) of mainly the Trebbiano grape, and a true D.O.C. Balsamico cannot have anything added. The "must" is then boiled down in open pots over a direct flame.
The extract (concentrated juice) from this cooking is now an intense fruity syrup. At this point some "mother" of vinegar is added. ("Mother" is composed of various yeast and bacteria especially mycoderma aceti, that cause a particular fermentation.) It is then aged for 12+ years in successive barrels of different aromatic woods - first in one, then transferred to another since, as it ages, the natural evaporation reduces the volume and a large barrel of Balsamico becomes a small intense fluid needing only a smaller "barrique" by the end of the process. Needless to say, real aged Balsamicos are therefore rather valuable, are presented in small bottles, and can easily cost more than fine wines.
Each company has its own secret progression of wooden barrels, usually including chestnut, cherry, ash, mulberry, oak and juniper. The finished Balsamico must be at least 12 years old, and some batches are nurtured for much longer. It is then presented to the D.O.C. (Denominazione di Origine Controllata), a governing body similar to those that govern the quality and origin of French and Italian wines. Balsamic vinegars without this designation on the label are mostly un-aged commercial products or some are aged with wood flavorings for 6 months to a year in stainless steel tanks, a few mid-range products are aged for 2 or more years in wooden barrels.
Since Medieval times, Balsamico was valued for its healing properties. Making perfect Balsamico was considered a form of art and had symbolic ties for Italian families. For example, new barrels were started when a child was born, nurtured for decades, and then given away at the eventual wedding. The balsamic story goes back some 900 years, to the Dukes of Este and other noblemen around Modena and in the province of Reggio Emilia. The Italian families treasured their reserves of balsamico and handed it down through generations. They presented the older vinegars (especially century old ones) only on very special occasions to their near and dear ones or sometimes to visiting dignitaries. Balsamico was stored in the family attic and tended to as meticulously as any other facet of the family estate, as it slowly matured into a liquid gold. Women of the family might be given a small cask as their culinary dowry. Balsamico came to be a symbol of peace and an extension of the hand of friendship from one family to another, and from one friend to another.
(Compiled by Daniele Giovannucci - www.dgiovannucci.net)