Aged Balsamic vinegar, (aceto balsamico) originated in Modena and Reggio Emilia Italy in the Middle Ages and is made from a reduction of cooked white Trebbiano grapes. As far back as 900 years ago, vintners in the Modena, Italy region were making balsamic vinegar which was taken as a tonic and bestowed as a mark of favor to those of importance. Although considered a wine vinegar, it is not a wine vinegar at all. It is not made from, wine but from grape pressings that have never been permitted to ferment into wine.
Traditional aged balsamic vinegar is produced from the juice of just-harvested Trebbiano white grapes boiled down to approximately 30% of the original volume to create a concentrate or must, which is then fermented with a slow aging process which concentrates the flavors. The flavor intensifies over the years, with the vinegar being stored in wooden casks, becoming sweet, viscous and very concentrated.
At the end of the aging period (12, 18, or 25 years) a small portion is drawn from the smallest cask and each cask is then topped up with the contents of the preceding (next larger) cask. Freshly reduced cooked must is added to the largest cask and in every subsequent year the drawing and topping up process is repeated. This process where the product is distributed from the oldest cask and then refilled from the next oldest vintage cask is called solera or in perpetuum.