Why do some wines get better with age while others turn to vinegar?
Well, wines only turn to vinegar when they are fermented by acetic acid bacteria known as mycoderma aceti. Many wines have a bit of acetic acid in them, usually below the threshold of detection but not always.
What usually happens to wines as they age poorly is that they cook. This is not the fault of the wine, but rather the results of poor storage, say in a cupboard somewhere or a fancy rack in your kitchen. Sound familiar? OK, it may not be your fault, since a lot of wine retailers have equally crappy, if not crappier, storage but you get the idea.
That doesn’t explain why some wines get better with age. In general, that’s due to the wine’s structure: acid, tannins, and sugar, as well as the quality of fruit in the wine.
It’s a result of many factors, such as the grape variety (some age well, others not so much), the terroir (some regions make more structured, and therefore more ageworthy, wines) and, of course, the winemaker. Some winemakers aim for an easy-to-drink, lush style of wine that may not improve in the bottle, while others may want a brutally tannic young wine that can last, and evolve for ages.