The yeast strains used to brew Ireland’s classic stout, Guinness, are genetically distinct from the ones used to make other Irish beers.
Brewer’s yeast (Saccharomyces cerevisiae) is an essential component of beer production. During fermentation, these microorganisms convert sugars from malt into alcohol and carbon dioxide. Using different strains of this yeast can result in different types of beer, such as stouts or lagers, and can even influence its flavour profile.
Daniel Kerruish at food and beverage company Diageo Ireland Unlimited and his colleagues investigated the evolution of the yeasts used to brew Guinness over the years based on records kept by the Guinness brewery on the yeast strains used in its malty, bitter stout since 1903.
The team compared the genomes of 13 strains of S. cerevisiae that are currently or have historically been used to brew Guinness, to 160 other strains, including six used in other Irish breweries.
Though the Guinness yeasts and the other Irish brewing yeasts belonged to the same lineage, Kerruish and his team found that the former were genetically different enough that they belong to a previously unidentified subpopulation. The non-Guinness Irish brewing yeasts were more closely related to strains that come from Britain.
The Guinness strains were also found to produce a specific balance of flavour compounds, such as 4-vinyl guaiacol, which produces a subtle clove-like aroma, and diacetyl, which imparts a buttery taste.
The team also found that the two strains currently used by Guinness are descendants of a strain used to brew the stout in 1903.
“The more we learn about the Guinness yeast the more we realise how unique and special it is,” says Kerruish. “Perhaps we shouldn’t be surprised since Guinness is an amazing beer.”
“What is particularly unique and exciting in this work is that the company has quite detailed records on the historical handling of the strains,” says Brian Gibson at the Technical University of Berlin, Germany. “This information could potentially be used to further develop these yeasts or other yeasts used in industrial applications.”