Mother of vinegar is a cellulose that occurs naturally in vinegar as a result of bacteria. It is a harmless carbohydrate that can be filtered out of vinegar.
Although mother of vinegar is not harmful, many manufacturers pasteurize vinegar before packaging for resale to prevent the bacteria from forming. Vinegar that does produce mother of vinegar is not necessarily spoiled, however. Because of the acidic nature of vinegar, it does not need refrigerated but may change colors or develop sediment or haze, depending on the specific type of vinegar. White vinegar, for instance, remains mostly unchanged over long periods of time. Vinegar has an almost indefinite shelf life.