In 1857, Pasteur returned to the École Normale as director of scientific studies and continued his research on the problem. Notably, on April 20, 1862, he completed his first test of boiling and then cooling wine to kill the souring bacteria, a method of wine preservation (heating) that the Chinese first discovered as far back as 1117, though of course this was likely unknown to Pasteur.

At about this time, Emperor Napoleon III commissioned Pasteur to save the entire French wine industry, which had become overrun by “diseases” that caused the wine to be sour or bitter. In about 1863, Pasteur inspected a variety of wineries and came to the conclusion that “there may not be a single winery in France, whether rich or poor, where some portions of the wine have not suffered greater or lesser alteration.”

Continuing his research into heating the liquid, Pasteur, who patented his heating and cooling process in 1865, discovered that the wine could be saved from souring and the original flavor preserved by heating it to a mere 50-60 degrees Celsius or 122-140 degrees Fahrenheit. Quickly adopted by the wine industry, the general pasteurization process was not widely applied to milk for several years afterward, to the doom of many thousands, as raw milk at the time was particularly a common carrier of tuberculosis.