[7][8] During the explosion of scientific mycological studies in the 19th century, the yeast responsible for producing these so-called "bottom fermentations" was finally given a taxonomical classification, Saccharomyces pastorianus, by the German Max Reess in 1870.

[9] In 1883 the Dane Emil Hansen published the findings of his research at the Carlsberg brewery in Copenhagen and described the isolation of a favourable pure yeast culture that he labelled "Unterhefe Nr.

[13] Here Hansen classified a separate species of yeast isolated from the Carlsberg brewery as S. pastorianus, a name derived from and attributed to Reess 1870.

[17] Nonetheless, over the last decades of the 20th century, debate continued in scientific literature regarding the correct taxon, with authors using both names interchangeably to describe lager yeast.

[25] S. eubayanus has since been discovered in China, Tibet and Mongolia, further confirming both the existence of the species and its 99% genome similarity to the non-cerevisiae parent.

[26] As of 2014, most authorities have agreed that the bottom-fermenting yeast S. pastorianus was created by the inter-specific hybridisation between S. eubayanus and S. cerevisiae, but had not reached consensus on whether the mating event took place in Asia or Europe.

[27] Debate over taxonomy appears to have concluded, thus new research is now focused on the variation observed within members of S. pastorianus proper.

[28][29] In 2008 it was further concluded that the two groups were the result of two separate hybridisation events with the parent S. cerevisiae coming from a distinct ale/beer brewing origin.

Their findings were typical of similar studies, fermentation performance was more robust and the progeny/hybrids produced a mosaic of volatile sensory chemicals.