The age of balsamic vinegar: residence time and chemical descriptors

Traditional balsamic vinegar (TBV) production involves some distinct steps: the cooking of the must is followed by its alcoholic and acetic fermentation; then, during the aging in a barrel set, the volume loss due to evaporation is restored according to the technique of "rincalzo” (topping up). This procedure leads to a set of barrel containing a mixture of vinegars of different ages, so the real age of the finished product can only be defined as a “residence time” (RT), obtained as a weighted average among each aliquots of vinegar mixed through the years. From an algebraic point of view, the problem has been solved and the result is a mathematical model in which the TBV age is easily estimated from the volumes involved in the maintenance of the barrel set. While it is intuitive and commonly accepted that losses affect the yield of the barrel set, it is more interesting to clarify the relationship between yield, evaporation rate and age of TBV. The lower is the yield, due to losses by evaporation and other causes, the lower is the RT and thus the effective aging. The intensity of aging of TBV is indeed inversely proportional to the flow of vinegar through the barrel set.This simulation system has been modified by excluding the water, so the calculation can be based on the actual matter that undergoes aging, ie the solutes dissolved in the vinegar. To this end, the solute losses, due to chemical and physical phenomena and biological activities, have been quantified for every stages of TBV production.Based on the mass balance performed, a rigorous calculations can be set, in order to simulate the trend of the RT and concentration profile for the product. Yields calculated in this manner are consistent with data collected from different barrel sets for a few years and it is clearly evident that the yield significantly influences the RT of TBV: older TBVs correspond to high yields. The calculation of the RT on the basis of dry mass, besides being more correct because the aging process does not affect water, provides higher values than those calculated by the volume, and these differences are greater for the most aged barrels of vinegar. In short, increasing the yields of the aging process is equivalent to increase the quality of TBV.Several researchers tried to correlate the chemical composition to the age of TBV but no satisfactory results have been achieved. Recently, melanoidins start to seem a good indicator of TBV aging, since these compounds vary in terms of quality and quantity during the residence time of TBV in the barrels.(empty line