Saccharomyces pastorianus

Lore & Background

Bottom-fermenting strains of brewing yeast were described as early as the 14th century in Nuremberg and remained indispensable in Franconian and Bavarian brewing culture. In 1870, the German Max Reess gave the yeast its taxonomic classification, Saccharomyces pastorianus. In 1883, Emil Hansen at the Carlsberg brewery in Copenhagen isolated a pure yeast culture he labeled 'Unterhefe Nr. I', which he identified as identical to a sample donated by the Spaten Brewery of Munich in 1845. This yeast went into industrial production in 1884 as Carlsberg yeast no. 1. Hansen later reclassified this strain as Saccharomyces carlsbergensis in 1908, a name that continued to be used in scientific literature despite being invalid due to the precedence of S. pastorianus.

Reader's Guide

Saccharomyces pastorianus is significant as the key industrial yeast for lager beer production worldwide. Its hybrid nature, confirmed by DNA-DNA reallocation techniques in 1985, explained long-standing taxonomic confusion. The non-cerevisiae parent was identified as Saccharomyces eubayanus in 2011, with strains found in Argentina, China, Tibet, and Mongolia. The species is divided into two groups: Saaz type (allotriploid, with lost S. cerevisiae genome portions) and Frohberg type (allotetraploid, with near-complete genomes from both parents). Research in 2015 succeeded in creating novel lager yeasts by hybridizing selected S. cerevisiae with S. eubayanus, producing strains with improved fermentation performance. The species' legacy includes resolving debates over bottom-fermenting yeast taxonomy and enabling future strain diversification through hybridization.

Did You Know?

• The now-defunct synonym Saccharomyces carlsbergensis was attributed to Emil Christian Hansen in 1908, but the name Saccharomyces pastorianus (Reess 1870) has taxonomic precedence.
• The type strains of both synonyms S. carlsbergensis and S. monacensis are stored in yeast banks under the taxonomic name S. pastorianus.
• In 2011, the non-cerevisiae parent of S. pastorianus was identified as the newly discovered species Saccharomyces eubayanus, with a genome 99% identical to the non-cerevisiae portion.
• Himalayan strains of S. eubayanus carry several copies of the AGT1 gene, not found in Patagonian strains, with high similarity to S. pastorianus versions.