The process of making Balsamic vinegar begins when the grapes are absolutely ripe, they are harvested and then they are crushed and then pressed into a juice called “mosto”. At times if the sugar levels in the grapes are too low, the grapes are further ripened in a wooden box left in the sun for some time before crushing. The “must” is then cooked in open pots over a direct flame and allowed to simmer for 24 to 30 hours, until it becomes an intensely sweet concentrate, reduced in volume by one half or more. While it simmers, the sugars of the grapes caramelize slightly, giving the liquid an amber hue. This unfermented juice, called mosto cotto, is then cooled, allowed to settle, and, in accordance with the traditional methods, transferred to a “batteria,” which is a set of progressively smaller wooden barrels. These barrels are then stored in vinegar attics, called “acetaie” generally on the top floor of the house, to ferment, evaporate, and age over a minimum of 12 years and often decades. By this time it acquires a complex character — aromatic, intensely sweet and syrupy texture.
Although there is no fixed number of barrels required for a batteria, but a minimum of three are needed for the “must” concentration to undergo the processes that give balsamic vinegar its complex characteristics: transformation, maturation, and aging. The barrels, ranging in capacity from 10 liters to 100 liters, are fashioned from hard and soft woods such as ash, oak, chestnut, cherry, mulberry, and juniper. The barrels impart flavor and color to the concentrate, resulting in giving the vinegar a multilayered character. The choice of the variety of woods and their respective positions in the series is a matter of personal preference of the producers. There could any number of variations in this. The choices are typically dictated by personal preference and economic viability, as well as the density of the wood, porosity, flavor, and the availability.
Some producers prefer to use stronger, more aromatic woods for the small casks at the end of the series to impart a sharper finishing character to the vinegar in the final stages. Others favor the more neutral woods, which allow the vinegar to mellow. All barrels are highly porous and have large square bungholes covered by a cotton cloth to allow maximum exposure to air and assist oxidation and evaporation.