All wines contain acetic acid, the active ingredient in vinegar, but usually the amount is quite small—from 0.03 percent to 0.06 percent—and not perceptible to smell or taste. Once table wines reach 0.07 percent or above, a sweet-sour vinegary smell and taste becomes evident. At low levels, acetic acid can enhance the character of a wine, but at higher levels (over 0.1 percent), it can become the dominant flavor and is considered a major flaw. A related substance, ethyl acetate, contributes a nail polish-like smell.
A sweet, vinegary smell that often accompanies acetic acid. It exists to some extent in all wines and in small doses can be a plus. When it is strong and smells like nail polish, it's a defect.