4: Pasteurization

France was economically dependent on the wine industry, which was losing money because some wines spoiled during the process of fermentation (the process which alcohol is produced from sugar.)  Louis Pasteur, a former professor of physics and chemistry, was commissioned to discover what was causing this wine to go bad.  He eventually proved that microorganisms, or organisms that were not visible to the naked eye, were causing the wine to spoil. He devised a solution in which wine could be gently heated and then cooled.  This process kills the harmful microorganisms and allows for the production of wine.  

Not only did he solve a major problem for the wine industry, but his method, later named pasteurization in his honor, could also be used to prevent milk and other foods from spoiling. Today, the milk you buy at the grocery store is labeled "pasteurized" because of Louis Pasteur's research. His work spurred - a new branch of science called microbiology. Pasteur could have patented this process to become rich, but saw it necessary to share it with the rest of the world freely. 

Pasteur's study of fermentation inspired his germ theory, which influenced physicians to take more cleanly measures in surgeries and hospitals. Pasteur also discovered a rabies vaccine, setting the principles and foundations for a new science known as immunology.