Pasteur founded the science of microbiology and proved that most infectious diseases are caused by micro-organisms. This became known as the "germ theory" of disease. He was the inventor of the process of pasteurisation and also developed vaccines for several diseases including rabies. The discovery of the vaccine for rabies led to the founding of the Pasteur Institute in Paris in 1888.
When he was only twenty-six years old Pasteur solved a problem that had been puzzling the great chemists of the day. He found that when light was passed through tartaric acid - this was found in wine dregs, it produced a strange effect. Pasteur proved that this was because the acid is actually not one acid but a mixture of different acids. This find impressed the scientists of influence and established Pasteur's reputation.
While at the University of Strasbourg he became interested in fermentation and this interest continued when he moved to the University of Lille. The faculty had been established partly to serve as a means of applying science to the problems of the industries of the region, especially the production of alcoholic drinks. This work in fermentation enabled Pasteur to identify that the changes brought about when beer or wine ferments, milk turns sour or meat decays, occur when special micro-organisms are present.
As a result of these findings Pasteur was asked to help the local breweries where the beer had turned bad. The souring of wine and beer was a major economic problem in France. Pasteur looked at some droplets of bad beer through a microscope and observed that the beer contained small rod shaped bacteria, instead of round yeast cells. Although micro-organisms are essential in fermentation they must be the right ones. This was a major discovery. Pasteur made brewing a more scientific procedure and showed brewers how to culture the right organisms for good beer. He also demonstrated to the wine industry that if wine is gently heated to sixty degrees celsius for a short time, the growth of harmful bacteria is prevented and the wine does not go sour in bottles or barrels.
Pasteur then extended this to other problems such as the souring of milk. He proposed heating the milk to a high temperature and pressure before bottling. The process is now in widespread use and is called pasteurisation.