Yes, plum vinegar can go bad. The vinegar will start to ferment and produce a sour smell.  If left untreated, the vinegar will eventually spoil and become unusable. It is essential to discard any spoiled vinegar to avoid food poisoning. This is how to tell if plum vinegar has gone bad: - If the color of the liquid has changed and become darker. - If there are signs of mold on top or at the bottom of the bottle. - If it smells differently than usual (although it should smell like plums). -If you notice any change in taste, it's probably best to discard plum vinegar. Plum vinegar will typically last for about two years before going bad. However, this will depend on how you store the vinegar.  If stored improperly, the shelf-life of plum vinegar may be significantly less than two years.