Vinegar is a sour liquid used to flavor and preserve food. The taste comes from acetic acid, which forms at least 4% of the total volume.
Vinegar is made by fermentation of wine, cider, or any other alcohol solutions; bacteria (Acetobacter and Acetomonas) oxidize the alcohol (ethanol) to acetic acid. The formation of vinegar by bacterial action is a batch process, and when each batch has been oxidized a small quantity of the product is left in the cask. This residue contains sufficient bacteria to start up oxidation in the next batch.
Malt vinegar is produced from alcohol fermented from potatoes or cereals. Malt vinegar is brown, whereas vinegar made from poor wines is red or amber.