The production of balsamic vinegar is a lengthy process. Like wine, it must be aged and fermented over time. It involves years of alcoholic fermenting, transferring from one container to the next and repeated adaptations and adjustments to produce the end result.
In Italy, 12 years minimum fermentation is required to label a product as “traditional” balsamic vinegar though the fermentation process can last up to 25 years. When done correctly and with care, the manufacturing process of balsamic vinegar produces a product that is unique and useful in a variety of culinary applications.
Balsamic vinegar uses grapes, traditionally white grapes, which are boiled down in a special process until the result is 30% of the original volume. This concentrated juice is the “must,” which will then be stored to begin fermentation.
The must is placed in large storage tanks or wood barrels for fermentation. Yeast is added or allowed to grow spontaneously to convert sugar into alcohol. Enzyme activity does much of the initial work. Either an acetobacter or strong wine vinegar is added for acidity. The acetobacter eats the alcohol, converting it into vinegar.
A series of barrels in decreasing sizes is called the “batteria.” The must, once properly fermented, is poured into the largest barrel at somewhere near 70% capacity. This ensures sufficient air for continued oxidation. 15% to 30% of the liquid will evaporate each year, shrinking the contents of the barrel. At the end of the year, the contents of a barrel are transferred to the next size down until several years later when the last barrel is ready to be poured out as balsamic vinegar.
As the water continues to evaporate from the product, the vinegar mellows, developing a strong sweet aroma. Usually, this process is performed in the heat of the summer, to increase microbial activity.
In Modena and Reggio, Italy, balsamic vinegar is manufactured in the ideal conditions of extreme fluctuations of temperature with hot summers and cool winters. Periodically, the manufacturers will make adjustments to the acidity or sugar levels for the best results. It is perhaps no surprise that with the difficulty and amount of time required to produce traditional balsamic vinegar, bottles can cost from $150 to $400 in U.S. dollars.