If you’ve ever had milk, you’re probably familiar with the work of Louis Pasteur, the 19th-century French chemist and biologist. He prevented diseases, developing a process — widely known as pasteurization — for killing microbes in milk and wine. He also created vaccines for rabies and anthrax. And his ideas led to the acceptance of germ theory, the notion that tiny organisms caused diseases like cholera. Pasteur even helped us brew better beer.

“He’s considered the benefactor of mankind,” said Joseph Gal, a chemist and professor emeritus at the University of Colorado.

But before all that, Pasteur was an artist. And without his early creative explorations, he may not have made one of his most monumental, but least talked about, discoveries in science, one with far-reaching implications.

In a paper published last month in Nature Chemistry, Dr. Gal explains how a young Pasteur fought against the odds to articulate the existence of chirality, or the way that some molecules exist in mirror-image forms capable of producing very different effects. Today we see chirality’s effects in light, in chemistry and in the body — even in the drugs we take.