On Food and Cooking

simultaneously converts a portion of the
abundant grape sugars into alcohol, and that
alcohol into acetic acid. These conversions
proceed slowly, over the course of several
years, because the high concentration of grape
sugars and acids inhibits the growth of all
microbes. The alcoholic fermentation is
carried out by unusual yeasts,
Zygosaccharomyces bailii or bisporus, that
are adapted to surviving in environments high
in sugars and in acetic acid. At the same time
that the two fermentations take place, so do
the processes of maturation and aging.
In the end, traditional balsamic vinegar
may contain anywhere from 20 to 70%
unfermented sugars, about 8% acetic and 4%
tartaric, malic, and other nonvolatile acids, an
aroma-enhancing 1% alcohol, and up to 12%
glycerol, a product of the yeast fermentation
that contributes to the velvety viscosity.
The “condiment” grades of balsamic
vinegar are made much more rapidly than the