Is vinegar with a cloudy, slimy sediment at the bottom still usable?
Nearly all commercially made vinegar will last indefinitely in an unopened bottle. Once opened and exposed to air, however, harmless “vinegar bacteria” may start to grow. This bacteria causes the formation of a cloudy sediment that is nothing more than harmless cellulose, a complex carbohydrate that does not affect the quality of the vinegar or its flavor. We confirmed this with a side-by-side comparison of freshly opened bottles of vinegar and those with sediment (strained before tasting).
The Vinegar Institute carried out storage studies of vinegar and determined that the shelf life of opened vinegar stored in a dark cabinet at room temperature is “almost indefinite.” To deal with the unsightly sediment, simply strain the vinegar through a coffee filter set inside a fine-mesh strainer before using it.