Red wine vinegar is actually red wine that has soured or gone bad. Despite the fact that red wine vinegar is already sour grapes, it is still subject to further break down if not properly stored after opening. As yeast consumes the sugar in wine grapes, acetic acid forms. The acetic acid gives vinegar its recognizable taste. Exposure to air for extended periods of time leaves vinegar susceptible to evaporation, resulting in loss of flavor.
Remove the red wine vinegar from its present bottle if it contains a metal lid. Vinegar storage containers should be glass or ceramic with cork, glass or ceramic stoppers. Metal reacts with vinegar, resulting in corrosion.
Fasten the lid or stopper tightly. This will prevent air from entering the container and causing evaporation. Write the date of storage on a piece of masking tape using a waterproof marker and stick it to the underside of the bottle.
Store the closed red wine vinegar container in the refrigerator. If the bottle is too tall for your refrigerator, store it in a cool, dark cabinet. Red wine vinegar stored in the refrigerator will keep for six to eight months, while red wine vinegar stored in a cool, dark cabinet will keep for two to three months.
Sometimes red wine vinegar develops a cloudy hue. This is called the "mother" of the vinegar, a harmless bacteria. Straining with a coffee filter can remove this bacterium and you can continue to use the red wine vinegar afterward.
If vinegar smells or tastes rancid, throw it away immediately.