In chemistry racemization refers to partial conversion of one enantiomer into another. Chemistry (in Greek: χημεία) is the science of matter that deals with the composition, structure, and properties of substances and with the transformations that they undergo. ... In chemistry two stereoisomers are said to be enantiomers if they are mirror images of each other. ...

Asymmetric substances have two forms (at each point of asymmetry) which differ in their optical characteristics: the levorotatory form (the (-)-form) will rotate the plane of polarization of a beam of light to the left, while the dextrorotatory form (the (+)-form) will rotate the plane of polarization of a beam of light to the right. The two forms, which are mirror-images, are said to be enantiomorphic: each is the enantiomer of the other.

Many chemical processes take place without regard to a substance's optical characteristics, and result in a racemic mixture in which neither form predominates. However, pure forms of the enantiomers can be obtained: for example, by allowing crystalization, and hand-separating the left-handed and right-handed crystals. Biochemical reactions also prefer one form over another: most amino acids are asymmetric, and the L-form is used preferentially in biological systems.

Racemization is the process of a relatively pure substance becoming a mixture of enantiomeric forms; the rate of racemization (from L-forms to a mixture of L-forms and D-forms) has been used as a way of dating biological specimens.