Before germs, Pasteur's first great find was left-handed and right-handed crystals
Louis Pasteur is remembered for pasteurised milk and the rabies vaccine, yet some historians rate a much earlier discovery as his deepest. Peering at tiny crystals of tartaric acid salts in 1848, he noticed they came in mirror-image pairs, and so revealed that molecules themselves can be left- or right-handed.
Pasteur was born on 27 December 1822 in Dole, in the Jura, the third child of a poor tanner. An unremarkable pupil who preferred fishing and drawing pastel portraits, he fled a Paris boarding school from homesickness, failed an exam in 1841, and scraped a science degree with a mediocre chemistry grade. On his first try for the elite Ecole Normale Superieure he ranked too low, so he waited a year and entered in 1843 near the top.
The crystal puzzle was this: tartaric acid from wine twisted polarised light, while the synthetic version, chemically identical, did not. Pasteur saw that the synthetic batch held two crystal shapes, mirror images of one another, whose solutions twisted light in opposite directions and cancelled out. It was the first demonstration that a molecule could be chiral, an idea that later mattered enormously for drug chemistry.
At Lille, where he became science dean in 1854 and quipped that chance favours only the prepared mind, a local distiller asked for help with beetroot alcohol turning sour. Pasteur showed that living yeast, not mere decay, turns sugar into alcohol, and that a different microbe produces the sourness. Heating wine, and later beer and milk, to between 60 and 100 degrees Celsius killed most spoilers; he patented the process in 1865. His sealed-flask experiments disproved spontaneous generation, earning a 2,500-franc prize in 1862, and his ideas pushed Joseph Lister toward antiseptic surgery.
As director of studies at the Ecole Normale he could be a tyrant: after one threat to expel smokers, 73 of 80 students resigned. Three of his five children died of typhoid. He founded the Pasteur Institute in 1887, led it until his death on 28 September 1895, and lies in a vault beneath it, though his notebooks later showed he sometimes used deception against rivals.
Source: Louis Pasteur
