Pasteur, Louis (1822–1895), was a famous French scientist credited (among many other achievements) as the first person to understand the process of fermentation and the importance of microorganisms in the production and spoilage of beer. His observations on the heat treatment of beer to prevent microbial spoilage became known as “pasteurization.” Before Pasteur’s definitive statements on the nature of fermentation, it had been thought that the products of fermentation arose from “spontaneous generation,” which, in essence, propounded that “life” was continually being created out of inanimate matter. In 1860 Pasteur wrote, “Alcoholic fermentation is an act correlated with the life and organization of yeast cells, not with the death and putrefaction of the cells, any more than it is a phenomenon of contact, in which case the transformation of sugar would be accomplished in the presence of the ferment without yielding up to it or taking from anything.” By 1875 Pasteur had concluded that fermentation was the result of life without oxygen, whereby, in the absence of free oxygen in the atmosphere, cells were able to obtain energy which was liberated by the decomposition of substances containing combined oxygen.

In 1876 Pasteur published his groundbreaking book Etudes sur la Biere in which he dealt with the diseases of beer and described how the fermenting yeast was often contaminated by bacteria, filamentous fungi, and other yeasts. For example, long rod-shaped and spherical-shaped organisms (probably lactic acid bacteria) seen under the microscope were responsible for a sour defect. See lactic acid.

In Pasteur’s own words, “Every unhealthy change in the quality of beer coincides with the development of microscopic germs which are alien to the pure ferment of the beer” (1877). These unwelcome organisms had come into contact with the beer as a result of contamination in the production environment or through contaminated yeast. Pasteur observed that by holding beer at between 131°F and 149°F (55°C–60°C) for a short time the growth of beer spoilage organisms was inhibited and the beer could be rendered palatable for up to 9 months. This is the basis of the process of pasteurization.

Pasteur, it is said, was not a great lover of beer, but as a result of the Franco-Prussian War of 1870, the outcome of which resulted in France ceding the hop-growing region of Alsace-Lorraine, Pasteur had an animosity for all things German. This resulted in his determination to improve the quality of French-made beers, or as Pasteur himself stated, to make the “Beer of National Revenge”!

See also pasteurization.