Danish botanist who revolutionized the brewing (beer) industry by his discovery of a new method of cultivating pure strains of yeast.

Hansen, who began his working life as a journeyman house painter, received a Ph.D. in 1877 from the University of Copenhagen. Two years later he was appointed head of the physiology department at the Carlsberg Laboratory in Copenhagen, where he remained until his death. His research was concerned mainly with yeasts that convert carbohydrates to alcohol, and in 1888 he published an article that described his method for obtaining pure cultures (pure culture) of yeast. The yeast grown from these single strains was widely adopted in the bottom-fermentation brewing industries. Further investigations led him to the discovery of a number of species of yeast. He defined the characters of the different species and devised a system of classification. After further study he devised additional methods for the culture and isolation of certain species.