Examining glasses of spoiled wine in 1863, Pasteur remembered the microorganisms he’d seen in Bigo’s distillery years earlier. He theorized that the wine tasted sour because it had a disease, specifically unwanted bacteria.
Pasteur determined that yeast — critical to winemaking — had to be encouraged to grow, while unhelpful bacteria had to be killed. He found that heating wine to 50–60 degrees Centigrade did just that. He patented this method, called pasteurization, in 1865.
Pasteur also isolated the role of oxygen in winemaking. He developed a process that controlled how much oxygen came in contact with wine, and when — using both barrels and bottles.
“It is necessary to aerate the wine slowly to age it, but the oxidation must not be pushed too far. It weakens the wine too much, wears it out,” he wrote. “There exists a period…during which the wine must pass from a permeable container [the barrel] to one nearly impermeable [the bottle].”
Pasteur was credited with saving France’s wine industry. His 1866 essay “Studies on Wine” became the foundation of modern winemaking. Winemakers still use his process today, though they treat wine with sulfites rather than heat-pasteurizing it.
But more significantly for humankind, the chemist also used pasteurization to purify milk, cheese, beer and other products prone to spoilage.
Later in his career, Pasteur studied how germs cause disease in animals and humans, helping create the “germ theory of disease.” He created vaccines for chicken cholera, anthrax and rabies, ushering in the era of “preventive medicine.”
The father of microbiology, germ theory, pasteurization, and preventive medicine, Pasteur has saved incalculable millions of lives — but it all began with making better alcohol.