Can balsamic vinegar go bad? I reached for a bottle that had been in the pantry for about a year, and it had turned into globs of a jellylike substance. Was it usable?
— William G., via email
Vinegar in general has a very long shelf life.
Older bottles of wine-based vinegars might get sediment at the bottom, and sometimes they develop what is called "mother of vinegar," the natural mold used to make new batches of vinegar. Mother looks more like a thin sheet floating in the bottle.
Mother wouldn't be as thick as the globs you're describing, though. It's possible these are a byproduct of low-quality vinegar.
Balsamic vinegars vary wildly in price, from the truly aged balsamicos that can cost more than $100 a bottle to very cheap, balsamic-flavored vinegars that cost less than $5.
With the cheap stuff, manufacturers sometimes add caramel flavoring or sweeteners to mimic the true balsamic taste. Boiling cheaper balsamic with a little sugar makes it thicker and sweeter, too.
In this case, it sounds like the vinegar thickened up from sugar. It could be the cap wasn't tight, allowing the vinegar to evaporate.
If that's the case, it probably won't taste like it's supposed to, and you're better off just pitching it out. Next time, invest in a really delicious bottle of balsamic vinegar ($30 to $50) and use it sparingly to dress bitter greens or fruit, finish off a Parmigiano-Reggiano risotto or drizzle on a pork cutlet or grilled fish fillet.
Fine-quality balsamic is wasted in marinades or on very delicate foods like fresh mozzarella or prosciutto, which are overwhelmed by it. Similarly, a meal quickly becomes overshadowed by balsamic if it's used in more than one dish.