Vinegar consists of acetic acid, or CH3COOH, and water, H2O. Small amounts of sugar and fruit juices may be added to vinegar as flavoring agents, and infusions of herbs are also common.
While water makes up the bulk of vinegar's volume, acetic acid is the main active ingredient. The concentration of acetic acid in vinegar varies considerably from one variety to another. Distilled vinegar usually has the lowest concentration of acetic acid, at 5 to 8 percent by volume. Acetic acid concentrations in spirit of vinegar, a more concentrated form of vinegar, can sometimes go as high as 20 percent.