Fermentation occurs in the wooden barrel or in huge storage tanks. The cooked grape must is dispensed into barrels or tanks and an acetobacter called the ‘mother’ or some strong wine vinegar is added. The yeasts convert the natural sugar content into alcohol, which is consumed by the acetobacters and the result is vinegar. Typically, the process is started in late summer as the heat aids increased bacterial activity.
After fermentation, the vinegar is transferred to the batteria where the barrels are filled to 66 â€“ 75% of their capacity. The space left is for further acetic oxidation. During the first year, about 15 â€“ 30% of the volume is reduced due to evaporation. At the end the every year, the barrels are topped off from their larger counterparts and the largest is filled with new cooked must. This method of ‘topping up’ is called ‘rincalzo’. The transferring or graduating process, from barrel to barrel is known as ‘travasco’ which means ‘between barrels’. Rincalzo is done in the colder season when the level of bacterial activity is lowest. Also, because by the winter, the byproducts of the fermentation process precipitate to leave a clear liquid on top. Unlike wine, a wide range of temperature is beneficial to the balsamic vinegar as it helps in achieving the dense and complex nature. The vinegar attics in Italy, especially in the Modena and Reggio region, have an ideal climate as the summer is extremely hot and winter is very cold.
As the vinegar is transferred to smaller wooden casks, the water evaporates during the years and the vinegar mellows to a viscous, intensely sweet and aromatic fluid. The final balance of taste is made periodically to adjust acidity and sugar levels. This task requires years of expertise and can be done only by a skilled and experienced vinegar maker. After the larger barrels, the vinegar is shifted to tiny barrels for further ageing. In order to be labeled Aceto Balsamico Tradizionale under Italian mandate, the vinegar needs to be matured for at least 12 years.
Following years of vinegar maturing, the barrels have deposits called ‘patrimony’ at the bottom. It consists of the precipitates, used up yeasts, pieces of wood that have rubbed free and any other byproducts. This makes the older barrels so valuable that when they begin to deteriorate, they undergo a special barrel restoration process that involves building up wood around them. With careful preservation some barrels last for centuries.
Each process, be it the concentration, caramelization of the grape juice, fermentation, oxidation, continuous evaporation, or the 12 years of maturing in different woods, lends its own layer to the balsamic vinegar’s sweetness, sourness, intensity and earthiness. Because of the time intensive process and fiercely guarded recipes, production is quite low. After cooking down and evaporation of 12 years, only a fraction of the original volume remains. About 800 gallons of grape juice will yield only around 30 gallons of balsamic vinegar. This is why a 3 ounce bottle of balsamico can cost upwards of $100.
Aceto, Balsamico Tradizionale, Modena