How to Determine if Vinegar Has Spoiled

If a bottle of vinegar has a strange white film floating on top when opened, is the vinegar spoiled?

Actually, the film on top of the vinegar isn’t a sign of spoilage. This is called a “mother.” Vinegar mothers are gelatinous amalgamations of plant fiber from the vegetable or grain from which the vinegar was made and the acetic bacteria responsible for turning fruit and grain juices into vinegars. Vinegar needs bacteria and oxygen to form a mother; simply opening the bottle gives it access to both. Vinegar mothers come in a range of colors, from clear to black, and can be thick or thin. While the filmy mass floating on top will not harm the vinegar, it’s best to remove it before it sinks, because once at the bottom of the bottle, the mother can die and begin to decay, producing off-flavors and unpleasant aromas.

THE BOTTOM LINE:  If you find a filmy mass on top of your vinegar, just strain the vinegar into a clean bottle. If you find the filmy mass at the bottom of the bottle, give the vinegar a thorough sniff and taste it before using it.