The botanist Emil Christian Hansen (1842–1909) was born into a poor family in Ribe. As a young man, he initially worked as a house painter and later as a schoolteacher. Through a combination of hard work and chance, he enrolled at the College of Advanced Technology (now the Technical University of Denmark) and later at the University of Copenhagen, where his work on fungi attracted attention.

In 1877, the doctor and physiologist Peter Ludvig Panum (1820–1885) invited him to study the physiology of yeast at Panum’s laboratory. He was even given permission to work on his doctoral dissertation without having first earned an extended master’s degree – a rare recognition for a man of Hansen’s background.

At Panum’s laboratory Hansen studied the microorganisms that affect fermentation. His work caught the attention of the founder of Carlsberg, J. C. Jacobsen (1811–1887), who just a few years earlier had established the Carlsberg Research Laboratory in Valby with the goal of understanding the composition of beer. Jacobsen’s support enabled Hansen to work on his dissertation at the laboratory. Apparently, Jacobsen was so interested in Hansen’s work that eventually Hansen politely asked to be allowed to work without disruption. In 1879, Hansen completed his dissertation on organisms in beer and wort, and that same year he was made head of the physiological department of the Carlsberg Research Laboratory.

At the time, yeast was still a mystery to beer brewers. They knew that it was necessary but not how it worked or how to control it. Their work was based on tradition and experience, and results could vary widely from one brew to the next. Hansen’s approach was scientific. Under the microscope, he discovered that brewer’s yeast consisted of many different microorganisms and that contamination by unwanted ‘wild’ strains could lead to so-called beer sickness, resulting in poor, non-uniform beer. In the lab, he identified different strains of yeast and developed a technique for isolating and cultivating a single strain at a time. This was the first time that anyone had managed to isolate and cultivate pure yeast in a systematic and practical way.

In 1883, he was able to cultivate a highly robust strain, Saccharomyces carlsbergensis (now also known as Saccharomyces pastorianus), which ensured a consistent flavour across brews. The news travelled fast. Hansen proposed that brewer Jacobsen patent the cultivation method and sell the yeast to other breweries. However, true to his altruistic ideals, Jacobsen decided that both the method and the yeast should be shared freely with anyone who was interested, including competitors. As early as 1884, the famous Franziskaner brewery in Munich began to use the Carlsberg yeast. Soon, breweries in Berlin, Prague, Paris, the United States and Japan followed suit, and in less than 10 years Hansen’s approach became an international standard.

To Carlsberg, the discovery meant stable, export-friendly and competitive beer, and the Carlsberg brand became synonymous with high quality, just as Jacobsen had hoped. The Danish brewery tradition owes much to Hansen’s microbiological discovery, and today almost all lager in the world, including Pilsner, is based on yeast strains descended from the bottom yeast that Hansen cultivated as a pure strain in the Carlsberg Research Laboratory.

Hansen remained in his position as head of the physiological department of the Carlsberg Research Laboratory until his death, in 1909. His pure yeast strain is used in everything from dairy products to bread, wine and bio-fuel – and in pharmaceutical drugs, where yeast plays a key role in the production of insulin, among other products. An entire industry developed on the basis of Hansen’s research, which helped make Denmark a leading nation in beer and research.

The chapter is written by Asser Pelle.