Hansen, Emil Christian. Dr Emil Christian Hansen (1842–1909) was one of the first directors of the Carlsberg Laboratory, the research facility established in 1875 by the founder of the Carlsberg brewing company, J. C. Jacobsen. See carlsberg group. At this time the industrialization of the brewing process in general—and at Carlsberg in particular—had advanced to a stage where breweries had started bottling their beers themselves and exporting the bottled beers to foreign markets. This imposed entirely new demands on the microbiological stability of the beer, and work focused on the need to prevent beer from going sour before being consumed.

Hansen built on the work of Louis Pasteur, who had identified “impurities,” such as bacteria, wild yeasts, and molds, in the production yeasts used to ferment beers. Pasteur developed a simple heat treatment process, called “pasteurization,” to eliminate these contaminations in finished beer. See pasteur, louis and pasteurization. Hansen’s theory was that not only did the production yeasts contain impurities, but they also consisted of numerous populations of different yeast strains, out of which only a few were actually contributing optimally to the fermentations. This led Hansen to his truly revolutionary experimental work: He diluted the suspensions of yeasts he received from the Carlsberg production brewery, and then grew portions of the diluted suspensions in test tubes on sterile wort, continuing the dilution process until growth only occurred in a limited number of the test tubes. Hansen was convinced, correctly, that by this method he could isolate colonies of yeasts grown from a single cell. After a lengthy series of trial fermentations with his different isolates, Hansen was able to identify and grow the ones giving the optimal beer quality and process performance. In 1883 the work was completed and, at the Carlsberg Brewery, for the first time in history, commercial beer was brewed using a pure culture of the best lager yeast available, which was duly named Saccharomyces carlsbergensis (now known as Saccaharomyces uvarum).