Sep201110
Joe McPhee
5
The origins of lager brewing
Although I spend an inordinate amount of time chasing down and thinking about new beer, in my day job, I’m employed as a microbiologist. So when I catch wind of something in my professional life that impacts my hobby, I tend to take notice. To that end, a recent publication in the Proceedings of the National Academy of the United States (PNAS, for the uninitiated) caught my attention. From the laboratory of Jose Sampaio at the Microbiological Resource Center in Caparica, Portugal, the study solves a long-standing mystery in the brewing world, namely the origin of the cold-tolerant portion of the lager yeast genome.
One of the first things you learn in the pursuit of good beer, is the difference between lagers and ales – to recap, ales are fermented at warm temperature and utilize a strain of yeast called Saccharomyces cerevisiae. This yeast is the same as that used in bread and wine making (although individual strains have important differences, they are still the same species). In contrast, lagers are fermented at cooler temperatures for a longer time, lending the finished product fewer esters and a generally “cleaner” product. The strain of yeast used for lagers is called, S. pastorianus (S. carlsbergensis in some older sources) long standing question has been, “What makes these strains of yeast different?”.
Lager yeast
Several groups have taken a crack at this problem, and a few years ago, the genome of the lager strain Weihenstephan 34/70 was sequenced, revealing that the strain was an allotetraploid – basically a hybrid, consisting of some genetic material from the ale-type S. cerevisiae and some genetic material from another yeast type (S. bayanus). This genome analysis revealed that the S. bayanus type DNA was important for several of the known characteristics of lager brewing, particularly sugar uptake efficiency, high sulfite production (that sulfurous flavour that some young lagers have is important for flavour stability), and production of sugar polymers that are important for yeast flocculation.
Even with this knowledge, it was unclear where the S. bayanus type DNA in the lager yeast genome came from… extensive surveys had never found a yeast that was identical to that found in the S. pastorianus. The Portuguese group seems to have solved this problem, identifying a yeast strain that is 99.5% identical to the S. bayanus portion of the domesticated lager yeast genome – a strain they term S. eubayanus. Intriguingly, although the well-established origin of lager brewing dates to 15th century Bavaria, the yeast found by the Portuguese group was found on beech trees in Patagonia.
Huh? Patagonia? This result was a little surprising to both the researchers and to others who follow this sort of thing, but it may make sense from an ecological point of view. Trees serve as hosts to a number of bacterial pathogens, some of which produce galls on the tree – these galls divert sugars from the plant to the pathogen, thereby giving the pathogen an energy source.
Beech tree gall - source of S. eubayanus. Photo credit: Diego Libkind
Yeast of the Saccharomyces genus are well-adapted to growing on concentrated sugar sources, and so these galls are often also colonized by yeast that make use of the abundant sugars present. Hardwood trees at middle/northern latitudes are often colonized by yeast that are tolerant of both cold (cryotolerant) and that prefer warmer temperatures (thermotolerant), due to the seasonal nature of the climate. In contrast, the beech trees on the Patagonia plateau experience more or less constant low temperatures year round (average temperature 6-8°C) and so we might expect selection for more cryotolerant species in this environment.
The authors propose that sometime during the 15th century, yeast from these Patagonian strains somehow made their way to a brewery and formed a hybrid with the ale-type S. cerevisiae then in use. These hybrids were then under positive selection within the brewery environment and became enriched over time. The main problem with this model as I see it is that there was no trans-Atlantic trade between Patagonia and Europe until at least the early 16th century with most settlement coming much later. This discrepancy leaves a sizable 150-200 year gap in the record between the recorded beginnings of lager production in Bavaria and any sizable trade between Europe and Patagonia. Although it’s clear that the authors have found the true source of the non-cerevisiae portion of modern brewing strains (genetics doesn’t lie), I suspect that these strains evolved after the original low-temperature brewing strains that were in use from ~1400-1600. It is possible that other hybrids of cold-tolerant European yeast may have formed early but have since been lost due to competition from better adapted Patagonian hybrids. Further molecular archaeology may shed further light on these possibilities (anybody out there have any samples of lager from the 15th century?). No matter how you slice it – the discovery of the yeast responsible for lager production is something worthy of raising a toast. Prost!
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5 Comments to “The origins of lager brewing”
[...] The origins of lager brewing From the laboratory of Jose Sampaio at the Microbiological Resource Center in Caparica, Portugal, the study solves a long-standing mystery in the brewing world, namely the origin of the cold-tolerant portion of the lager yeast … Source: maltedmusings.hoppress.com [...]
First of all Joe, great write up. You make microbiology sound a lot less menacing.
Second, I am completely out of my field of knowledge here, so I apologize if my questions are ignorant.
The incongruent time lines still worry me. How can we be sure about directionality? As I asked in an early thread:
Why isn’t that the missing link yeast went to S. America and found a safe haven while going extinct in Europe (can a yeast go extinct?)?
Similarly, can 150-200 years of lager brewing be easily replaced by the Patagonian yeast such that we have no other record of the preceding yeasts? Can we really account for current lager yeast strains to have come from one small place thousands of miles away, which traveled to Europe, then made its way into brewing, and finally imbedded itself so strongly that there is no sign of the previous cryotolerant yeasts?
I appreciate your feedback.
Those are great questions Eugene. The most important thing to get to directionality though is that the brewing yeasts are hybrids. The Patagonian yeast didn’t “replace” the ale-yeast, they combined with it to become something else entirely. You can’t find the Patogonian yeast in brewing environment, you can just find evidence in the current yeast strains that it must have once been there. The modern lager (S. pastorianus) contain a typical ale yeast component as well as a component that gives them lager-promoting activities (that’s what the term allotetraploid refers to – it has 4X the number of chromosomes as a typical strain and they come from different sources). The chromosomes of the domesticated lager yeast have also recombined with the S. cerevisiae chromosomes in several sections – indicating that they’ve spent some time together. When it comes to hybrid production, these are typically one-way roads. I don’t know of any examples of hybrid genomes spontaneously dissembling into the original component chromosomes and recreating a diploid genome (although this may be possible).
It’s harder to imagine that a brewing strain would escape the brewery and go on to infect millions of Patagonian trees than to imagine it occurring in the reverse direction (or maybe I just don’t have much of an imagination). As far as your last question – with evolution, we can only observe what we have in front of us, whether is fossil bones or genetic evidence. We can’t say what strains may have existed before this one came to dominate lager production, but we do know that within a brewing environment there is a lot of selection for yeasts that perform well and a lot of competition for those that don’t. Even a small change in fitness combined with billions of generations of yeast propogation, would result in unfit strains going extinct. The 150-200 years thing is a back-of-the-envelope calculation. I don’t really know when the first true lagers were produced – we just know that people were brewing in cooler caves ~1400-1450 and that in 1553 Bavaria outlawed summertime beer production (presumably because they liked the low-temperature product better).
I’m completely serious about the old samples too – I’ve got a collaborator here who specializes in ancient DNA analysis (we’ve got a paper coming out in Nature next week that (I think) is going to get a shitload of press) and I’d love to be able to look at how lager brewing actually came into being (i.e. pre-European/American trade).
I still don’t believe that this is the actual yeast that hybridized in Germany. Isn’t there a possibility that a yeast with the same genetics to contribute existed in Europe at that time?
Not really – at least not according to the genetic data. It is possible that there was another lager-type strain that was eventually succeeded by the hybrid they describe (I actually suspect that’s what happened), but again, you’d need samples of beer from the 15th century to resolve that.