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===''S. pastorianus''===
Commonly known as lager yeast to brewers, this yeast is a hybrid of ''S. eubayanus'' and ''S. cerevisiae'' <ref name="wikipedia_cereisiae" />. ''S. pastorianus'' is named after the first description by Max Reess in 1870 following his work with German breweries utilising utilizing bottom-fermenting lager yeast, naming it originally after Louis Pasteur.
For a long time the origins of the hybrid were unknown and was were postulated to be a hybrid between ''S. cerevisiae'' and ''S.uvarum'', or ''S. cerevisiae'' and ''S.bayanus''. Recent work eg. Libkind et al 2011 proved that the hybridisation was between ''S. eubayanus'', which had been recently found in South America and ''S. cerevisiae'' <ref name="libkind_2011" /><ref name="bing_2014" />.
Emil Christian Hansen was the first in the world to isolate a single pure strain of ''S. pastorianus'' while he was working at the Carlsberg brewery, leading to its the synonymous classification name, ''S. carlbergensis''. The type that Hansen isolated was a Saaz type, and it's believed that Saaz types are also prevalent in Bohemian / Czech ''S. pastorianus'' strains while German types are typically Frohberg. ([https://onlinelibrary.wiley.com/doi/full/10.1002/yea.2960] , [https://genome.cshlp.org/content/18/10/1610.full] )
With recent whole genome sequencing data, it has been discovered that some strains of commercial yeast have been misidentified as either lager yeast or ale yeast. [http://sykesey.id.au/?p=20 Ben Sykes reported] that publicly available genetic data for an upcoming study indicates that WLP800, the Czech lager yeast from White Labs, is potentially ''S. cerevisiae'' (ale yeast). WLP029 German Ale/ Kölsch Yeast is potentially lager yeast.
[https://www.whitelabs.com/yeast-bank/wlp051-california-v-ale-yeast WLP051 California V Ale] yeast is also ''S. pastorianus''. Recent gene sequencing / PCR work has led to it being re-classified as a ''S.pastorianus'' yeast, though it has been used successfully for American-style Ale production.
==In Fermentation==