What was Louis Pasteur's first major research field?

What was Louis Pasteur's first major research field? Crystallography.

Louis Pasteur's first major research field was crystallography, the study of crystals and their structures. As a young scientist at the École Normale Supérieure, he investigated the relationship between crystal shape, chemical composition, and the rotation of polarized light.

His breakthrough came in 1848 while studying tartrate crystals. Pasteur noticed that crystals in a racemic mixture occurred in two mirror-image forms. He painstakingly separated the right- and left-handed crystals and showed that their solutions rotated polarized light in opposite directions. This work revealed molecular asymmetry and helped establish the foundations of stereochemistry and the modern concept of chirality.

Many people know Pasteur mainly for pasteurization, germ theory, and vaccines, but those achievements came later. His crystallographic research was not a side curiosity: it shaped his understanding of how microscopic structure produces measurable chemical behavior. In 1854, he moved into fermentation and microbiological research at Lille, beginning the phase of his career for which he is now best known.