It amazes me that there aren’t more desserts out there that call for balsamic vinegar, since when it’s good it’s not so much a vinegar as it is a syrup — an impossibly complex and delectable syrup. Run a “balsamic” search over at the Food Network site and you’ll come up with over 1300 different recipes, all but about 40 of them savory. But then the fact that so many American recipes — whatever their stripe — use balsamic vinegar is pretty darn impressive all by itself, especially when you consider that balsamic vinegar was virtually unknown outside the Italian towns of Modena and Reggio Emilia until around 1980.
Up until that time balsamic vinegar making was…well, it wasn’t a secret exactly, just something people in some northern Italian towns did in the privacy of their own homes. Go up into the attic of a typical house around Modena and it’s not unusual to find a small collection of casks of different sizes. In them are various distillations of grape juice, the smallest containing a dark, thick nectar that’s taken decades to mature.
Authentic balsamic vinegar takes more time to produce than any other foodstuff I can think of. Unlike regular wine vinegars, which were traditionally made by exposing wine to air until bacteria converted alcohol into acetic acid, balsamic vinegar starts with grape juice, simmered gently until it’s reduced to a thick, sweet liquid called mosto cotto, or “must”. This “must” must be first made into “wine” before it can be made into vinegar. Being very sweet, however, it’s too sugary for conventional bread or beer yeasts to live in. So, a special sugar-tolerant strain (zygosaccharomyces) is added to initiate fermentation, which can take anything up to eight months.
Once the alcohol level of the must reaches about 9%, acetic acid bacteria are allowed to move in to start the acidification process. The must is poured into the largest of the series of casks through a square-shaped hole in the top (a hole that’s never plugged, just covered with cloth). All the casks in the line have holes like these, so air can get in and moisture can get out.
Once a year (usually in the cold winter months when the bacterial activity is down and the vinegar is nice and clear) a little — and it’s always very little — finished balsamic vinegar is drawn from the smallest cask. That amount (plus the volume of whatever water has evaporated) is replenished by pouring in a little vinegar from the next biggest cask. That’s replenished by vinegar from the next biggest cask, and so on, until the very largest cask is topped of with fresh-fermented must. As you can imagine, if you only draw off a few ounces of vinegar a year, and the smallest cask holds a gallon or more, that stuff sits there for quite some time.
Over the years the vinegar not only develops its own flavor, it absorbs it from the wood of the cask. That being the case, each cask in the series is usually made from a different type of wood. More and different woods, after all, mean more and different flavors. A typical balsamico maker might employ casks made from oak, chestnut, cherry, ash, juniper, mulberry and acacia. The order in which those casks are employed varies from family to family, and (as you might expect) is the subject of much debate among the balsamic vinegar cognoscenti.
Of course finding some of this really, really good stuff is pretty darn near impossible for a mere mortal. If you do you can expect to pay upwards of $700 for a mere 3 1/2 ounces (100 ml.) of it. But of course you’d never waste a vinegar like that on something like a pear tart. You’d just sit it on your mantlepiece, where it would be guarded by trip wires, attack dogs and laser-beams, forever.