It has been seen that pyruvate acid is converted either into ethyl alcohol or lactic acid in the absence of oxygen (anaerobic condition). In the presence of oxygen (aerobic condition), however its metabolism is different. Pyruvic acid is oxidized to acetyl-CoA, which then undergoes a series of changes referred to as Krebs citric acid cycle.
The citric acid cycle is also called as the tricarboxylic acid cycle (TCA cycle) since citric acid is a tricarboxylic acid, i.e. with three-COOH groups. Each cycle results in the conversion of one molecule of acetic acid, in the form of acetyl-CoA, to carbon dioxide and water.