A fermentation product of wine. During fermentation, certain bacteria produce acetic acid by oxidizing alcohol when exposed to air. VINEGAR contains 4 percent to 6 percent acetic acid, which gives vinegar its characteristic sour taste. As vinegar, acetic acid is a common ingredient in food preparation. One of the simplest organic acids, acetic acid contains only two carbon atoms. It is classified as a weak acid because it is only partially ionized, unlike strong mineral acids, such as hydrochloric acid.

Acetic acid plays a pivotal role in metabolism. To be metabolized, acetic acid must be activated as acetyl CoA, in which acetic acid is bound to a carrier molecule, COENZYME A, which is in turn derived from the B vitamin PANTOTHENIC ACID. Metabolic pathways that oxidize fatty acids, carbohydrate, and amino acids for energy, all yield acetyl CoA, the common intermediate by which carbons from these fuels enter the KREB’S CYCLE to be oxidized to carbon dioxide. Alternatively, acetyl CoA can be used as a building block. It forms saturated fatty acids, cholesterol, and ketone bodies. Nerve cells can use it to form the NEUROTRANSMITTER, ACETYLCHOLINE. Tissues combine acetic acid with amino sugars to form a family of sugar derivatives like Nacetylglucosamine and N-acetylgalactosamine that help define recognition sites on the surface of cells and blood group specificities, such as the A, B, O, and Lewis blood groups used in blood typing.