French scientist Louis Pasteur disproved the theory of spontaneous generation, the idea that certain organisms are ever-present in nature. For example, early scientists believed fleas came from dust and maggots from dead meat absent anything else.
Pasteur theorized and later proved that all organisms come from something else, that nothing exists in a vacuum. He extended his line of thinking to the realization that bacteria can cause problems. For example, grape juice will turn to vinegar instead of wine.
Killing the bacteria, Pasteur reasoned in 1864, results in grape juice that will always ferment into wine rather than vinegar. Pasteur’s methods involved raising the temperature then storing in a clean environment, a technique that became known as pasteurization.
In 1882, Robert Koch discovered bacteria in milk was responsible for anthrax and these spores could be killed by Pasteur’s methods (winning him a Nobel Prize). Pasteurization applied to milk by chemist Earnest Lederle in 1810. Pasteur was also known for creating vaccines for anthrax and rabies. Through his discoveries about bacteria he also started the practice of keeping medicine clean. Pasteur died wealthy and famous but not from pasteurization.