II.

Work on Fermentation

After spending several years of research and teaching at Dijon and Strasbourg, Pasteur moved in 1854 to the University of Lille, where he was named professor of chemistry and dean of the faculty of sciences. This faculty had been set up partly to serve as a means of applying science to the practical problems of the industries of the region, especially the manufacture of alcoholic beverages. Pasteur immediately devoted himself to research on the process of fermentation. Although his belief that yeast plays some kind of role in this process was not original, he was able to demonstrate, from his earlier work on chemical specificity, that the desired production of alcohol in fermentation is indeed due to yeast and that the undesired production of substances (such as lactic acid or acetic acid) that make wine sour is due to the presence of additional organisms such as bacteria. The souring of wine and beer had been a major economic problem in France; Pasteur contributed to solving the problem by showing that bacteria can be eliminated by heating the starting sugar solutions to a high temperature.

Pasteur extended these studies to such other problems as the souring of milk, and he proposed a similar solution: heating the milk to a high temperature and pressure before bottling. This process is now called pasteurization.