"Did you ever observe to whom the accidents happen? Chance favors only the prepared mind."
Louis Pasteur, French chemist and microbiologist
At the beginning of the 1860s French chemist Louis Pasteur (1822-1895) observed that living cells, known commonly as yeast, were responsible for forming alcohol from sugar and, when contaminated, led to its souring. He was able to distinguish and separate these microorganisms, and, in 1862, he and French physiologist Claude Bernard (1813-1878) showed that most of the bacteria present in milk could be killed if the milk was heated to 145°F (63°C) for thirty minutes. The milk was then rapidly cooled to eliminate bacterial contamination. Pasteur applied the same principle to beer, the souring of which was a sore point in the French economy. This process of extended heating came to be known as "pasteurization."
Pasteur's revolutionary understanding of germ theory finally brought to an end the centuries-old notion of "spontaneous generation." Maggots did not "just appear" in decaying meat, according to Pasteur— they were the end products of microorganisms and bacterial infection. His proof that germs could cause fermentation and degeneration in liquids provided the framework for later research that led to cures for diseases in crops such as potato blight and various silkworm diseases, as well as anthrax and rabies.
