In the final quarter of the 19th century, no one in brewing was doing more cutting-edge research than Carlsberg.
In 1883, Emil Hansen isolated pure yeast strains there. In 1909, S.P.L. Sørensen developed the pH scale. Between those landmarks, in 1903, the researcher Niels Hjelte Claussen peered through his microscope and made his own discovery: a type of yeast cell distinct from the kind that made Carlsberg’s lagers and one responsible for the “peculiar and remarkably fine flavour” it made in the beer from which he cultured it.
That beer was an English stock ale, also known as old ale or barleywine. To honor the beer’s origin, he named his discovery the “British fungus”—Brettanomyces.