Vinegar is a sour liquid consisting mainly of acetic acid and water. The acetic acid content of vinegar varies from 4% to 12%, with most vinegars containing around 5% acetic acid. Acetic acid is a weak organic acid with the chemical formula CH3COOH. It is the second simplest carboxylic acid, after formic acid. Acetic acid is produced naturally by the fermentation of sugars by bacteria, and it is also produced synthetically. Vinegar is produced by the fermentation of ethanol or other sugars by acetic acid bacteria. The bacteria convert the ethanol or other sugars into acetic acid, which gives vinegar its sour taste. Vinegar has been used for thousands of years as a food preservative, condiment, and cleaning agent.