Lactic Acid

Lactic acid is a colorless, water-soluble liquid that freezes, or solidifies, at 64.4°F (18°C)—just slightly below normal room temperature. It is scientifically known as alpha-hydroxypropanoic acid and has the chemical formula C₃H₆O₃; the structural formula is shown below:

The "hydroxy" portion of the name tells chemists that there is an alcohol (OH) group in the molecule, and the "alpha" part of the name means that the alcohol is attached to the carbon atom adjacent to the acid (COOH) group. The "prop" portion of the name indicates that there are three carbon atoms. Lactic acid can also be called 2-hydroxypropanoic acid. Each of the two isomers rotates polarized light in a different direction: the L-isomer rotates light to the left, and the D-isomer rotates light to the right. Like most acids, lactic acid has a sour taste. It is found in sour milk, molasses, and many fruits. The lactic acid found in milk is usually a mixture of both isomers. It is used commercially in the textile and dairy industries. Lactic acid is the byproduct of anaerobic respiration, and is largely responsible for the aches in sore muscles after a vigorous workout.