Epic freshness episode with Special Guest Chris Quinn from The Beer Temple.
Wikipedia calls lager yeast Saccharomyces pastorianus, and notes that is is also sometimes referred to as Saccharomyces carlsbergensis, which is a great name, too bad it seems to have mostly been supplanted.
Brewers Association President Charlie Papazian’s The Complete Joy of Homebrewing refers to lager yeast as Saccharomyces uvarum, sometimes called carlsbergensis.
Then there’s Saccharomyces bayanus and Saccharomyces bayanus variation uvarum.
According to a recent scientific paper written by Diego Libkind and Chris Todd Hittinger, “The nomenclature of S. bayanus and S. uvarum has been confusing and controversial for decades.” In a presentation given to Latin American microbrewers Libkind even apologized on behalf of all his colleagues on the Systematics and Nomenclature Committee of the International Commission on Yeasts for the confusing state of affairs in lager yeast taxonomy prior to his recent research.
So what’s going on here? Is any one name correct? Are they all correct depending on the lager yeast strain? Fortunately for your dear readers, you’re about to find out. So grab a lager beer, and read on.
Lager yeast is Saccharomyces pastorianus (cryotolerant aka cold fermenting), and is a hybrid of Saccharomyces cerevisiae (ale yeast, see below) and Saccharomyces eubayanus (new proposed species, discovered in the Patagonia region of South America). S. pastorianus also used to be called Saccharomyces carlsbergensis. Pastorianus is named for Louis Pasteur, while Carlsbergensis is named from Carlsberg, the brewery where Emil Hansen isolated lager yeast between 1883 and 1885.
While modern lager yeast is a hybrid, there are three main beer related yeast species that are not, the two that comprise S. pastorianus (S. cerevisiae and S. eubayanus), as well as Saccharomyces uvarum (very similar to S. eubayanus ∼7% genome-wide sequence divergence). In other words, these three strains occur in nature, not just in an artifical (brewing) environment.
With me so far? Good. Or if not, maybe another beer is in order and try again. Feel free to switch to an ale if inclined, as we’ll be discussing ale yeast next.
Saccharomyces cerevisiae (thermotolerant aka warm fermenting) is the ale yeast used to ferment most ale and wine, and to leaven bread.
Saccharomyces uvarum (cryotolerant aka cold fermenting) is found in the wild in both Europe and the Americas, and at least according to the Libkind and Hittinger paper is “associated with beer as [a] contaminant” and “with cider or wine fermented at low temperatures”. This is species B strain in the paper.
Saccharomyces eubayanus (cryotolerant aka cold fermenting) is the new species proposed in the paper that was discovered in the Patagonia region of South America. Apparently Patagonian natives used to make a fermented beverage from the beech tree galls where the yeast was collected. The galls are created by Cyttaria, a parasitic fungus living on the beech trees that produces fruiting bodies rich in fermentable sugars, so this form of indigenous “beer” was actually a double fungus drink, with one fungus (yeast) fermenting another fungus (Cyttaria), which is kind of cool. This is species A strain in the paper.
Saccharomyces bayanus (cryotolerant aka cold fermenting) is, like S. pastorianus, a hybrid, but does S. pastorianus one better by being a triple hybrid of primarily S. uvarum and S. eubayanus (seems to vary between roughly 1/3 to 2/3 S. uvarum, with S. eubayanus making up the other 1/3 to 2/3, depending on the strain), with a dash of S. cerevisiae thrown in for good measure. S. bayanus is “associated with beer as [a] contaminant” according to the Libkind and Hittinger paper.
An interesting corollary to all this is that modern lager yeast is actually quite a bit younger than one might expect. The conventional wisdom, at least as I used to understand it, was that Germans started lagering (storing) beer in caves about 600 years ago, and that the cooler conditions selected for more crytotolerant yeast strains over time. While that may well be true as far as it goes, it appears that S. eubayanus must have traveled to the new world on some human related vector, such as timber, insects, clothing, barrels, or some such. This is because S. eubayanus does not appear to exist in the wild anywhere in the world except for Patagonia, and it needed to be present in Europe sometime before Hansen first isolated lager yeast in the late 19th century. Thus, the window for a hybridization event between Saccharomyces cerevisiae and Saccharomyces eubayanus is roughly bookended by the start of new world exploration by the Europeans around 1500 and the isolation of lager yeast a bit before 1900. Libkind’s best guess is that the event occurred sometime between 1600 and 1800, and I like to imagine a fairly tame domesticated S. cerevisiae strain getting cozy in a barrel of lager in a Bavarian cave somewhere when a wild eyed S. eubayanus strain bursts in and has it’s way with the unsuspecting old world yeast cell, creating a whole greater at making tasty, cold-fermented beer than the sum of its parts.
Hopefully that sheds a bit of light on lager yeast and the scientific nomenclature surrounding it. Here are some additional interesting tidbits on where the various scientific words come from:
The roots of the word Saccharomyces basically mean “sugar fungus”. (Greek sakkharon, sugar) and [Greek mukēs, mukēt
Similarly, Brettanomyces is “British Fungus”.
Despite the Greek ending, genus names ending in -myces sometimes refer to bacteria, because they were originally thought to be fungi. Examples are Saccharomyces (Greek sakkh
Cerevisiae is based on Ceres, the Roman
god goddess of grain - Cerevisiae apparently literally means beer in Latin.
LA Times article on the Libkind and Hittinger paper http://articles.latimes.com/
Scientific paper written by Diego Libkind and Chris Todd Hittinger et al: http://www.pnas.org/content/
Presentation given by Diego Libkind at the Latinoamerican Microbreweries Conference in late 2012 entitled “Domestication of Brewing Yeasts and the Patagonian origin of Lagers strains: Saccharomyces eubayanus” http://beerdownload.com/LagerYeast.pdf
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