I’m surrounded by hundreds of people—maybe 600, maybe more—who are all drinking great mugs of foamy lager. Some struggle to hold the liter glasses; others wrap a big hand around theirs and gulp. With a deep blast of a tuba, followed by an accordion’s bright wheeze, the brass band starts into another round of songs, and the drinkers seem to lift their glasses in time to its cadence.
I’ve been to Munich’s Hofbräuhaus dozens of times, but I never quite get used to it. It’s so vast, so loud, so busy, so storied. Hustling waiters, carrying four full mugs of lager in one hand and hoisting trays of food over their shoulders, barge through the crowds of visitors who see this place through their phone screens, sending videos home to friends.
After I find a seat and order, a liter glass is slammed down onto the wooden bench in front of me. Most people are drinking the brilliant golden helles lager, but today I’ve gone for the dunkel, the dark lager. It’s red-edged with an off-white foam, and has the classic toasted-bread-crust flavor of Munich malt, with the essential crispness that drinkers have come to expect in a lager.
It may be touristy, but the Hofbräuhaus remains one of the most important places in the world for lager. The building is a monument in the beer’s long story, and being here recalls generations of people before me who’ve drunk brown beer from big mugs right where I’m sitting. But more than that, the venue—formerly the old Bavarian royal family brewery—is tied to one of the most enduring lager mysteries.
Today, lager is an extraordinary international triumph. Go almost anywhere in the world and ask someone to explain “beer,” and they’ll likely describe a pale lager—bright, bubbly, and refreshing. Arguably the greatest success of lager is that it became so knowable, and so trusted. Pretty much wherever you go, you can order a lager and know what you’re going to get, and how it will feel to drink it.
And yet, for all of its familiarity, there is an enigma at the core of lager’s long story, one that has fascinated and frustrated me for years: We don’t know where lager yeast came from, or how it developed.
No matter how much scientists and historians have searched—and they’ve literally hunted in forests, cellars, and old brewery buildings, and have run all the DNA testing that’s available to them—a void has existed at the heart of what is the world’s most popular and most consumed beer.
But just within the last year, the latest detective work and scholarly research have led to a compelling new theory about lager’s true origins. After many centuries—spanning lager’s 14th-century beginnings to its present-day ubiquity—have we finally solved the foundational mystery behind the world’s best-loved beer?
The short version of lager’s origin story is that somewhere in northern Bavaria, probably in the 14th century, brewers rolled barrels of fresh beer into cold cellars.
Those cellars were sometimes dug beneath towns, sometimes into hillsides. They were nature’s refrigerators, holding a constant cool temperature and used to keep food and wine, and then beer. Storing beer in these cool cellars, and leaving it for longer than was typical for other beers, became a standard practice throughout Bavaria.
While we don’t know exactly why this method of cellar storage originated, it likely persisted because people simply wanted consistent, good-quality beer, and wanted to drink it year-round.
“Go almost anywhere in the world and ask someone to explain “beer,” and they’ll likely describe a pale lager—bright, bubbly, and refreshing. Arguably the greatest success of lager is that it became so knowable, and so trusted.”
As 14th-century brewers would have discovered, the cold, slow maturation period helped remove negative characteristics and compounds from the beer, like buttery diacetyl, clove-like phenols, and pungent sulfur. It also would have reduced rougher flavors from the smoky malt, and any bacterial funk. Plus, we have to imagine that drinking a chilled beer directly from a cool cellar was a wonderful experience—and a rare one in the centuries before artificial refrigeration.
Brewing also didn’t take place during the summer months, again in pursuit of consistency. In the warmer weather, batches of beer soon spoiled, plus there were increased fire risks from malting barley during dry conditions. But cellar-stored beer would have kept all season long, and slaked drinkers’ thirst throughout the hot months of the year.
Those cellars eventually gave their name to the beer (lagern means “to store” in German). It’s important to distinguish between the process of lagering—the act of putting beer in cellars—and lager as a type of beer made with a specific species of yeast. It’s believed that the lagering process predated lager yeast by more than 200 years, so the great beer mystery we’re trying to discover is how, when, and where they came together—and what happened next.
We know little about those early, cellared beers, those ancestors of today’s lager. They were probably dark and sweet, moderate in alcohol, and more nourishing than intoxicating. They were almost certainly fermented with a mix of different yeasts, or a stellhefen, a mixed culture including Saccharomyces cerevisiae—traditional ale yeast—as well as other wild yeasts, and probably bacteria.
We know that the stellhefen would not have remained static: Yeast is a living organism that evolves and adapts to its surroundings, with different strains finding their way in and out of breweries with the movement of seasons, people, ingredients, and barrels. Some of those yeast strains are cold-tolerant, so they would have thrived in the cellars, outcompeting other strains that were less adapted to that environment. This process was accelerated by human intervention, with brewers choosing to reuse yeast from only the most successful batches of lager.
These were the conditions in which a new beer yeast species emerged: Saccharomyces pastorianus, or what we’d colloquially call lager yeast. That yeast would go on to change the history of beer. And finally, we think we know how, where, and why it first appeared.
“The progenitor of today’s lager yeast comes from Germany, the yeast is a hybrid species, and the hybridization event happened in a brewery setting,” says Kevin Verstrepen, professor and director of KU Leuven Center for Microbiology and one of the world’s leading yeast researchers.
Through genetic profiling, we know that the parents of Saccharomyces pastorianus are Saccharomyces cerevisiae (ale yeast, which performs best in ambient temperatures, fermenting quickly and efficiently) and Saccharomyces eubayanus (a cold-tolerant wild yeast that is inefficient at fermenting certain malt sugars).
Saccharomyces cerevisiae and Saccharomyces eubayanus are different species of yeast, and their pairing is the microbial world’s version of a lion and tiger breeding. It’s not impossible, but it requires specific circumstances to happen, and the resulting progeny—the liger, lager yeast—is a distinct new species with genetic traits from each parent.
“You have a parent bad at cold fermentation but great at eating sugars, and you have a parent bad at eating sugars but great at growing at cold temperatures,” says Fábio Faria-Oliveira, R&D Manager of White Labs Inc. “You push those cells together, put the stress on them, and eventually two of them will do something different to everything else.” It’s called rare mating.
That mating—a singular occurrence, a one-night stand of sorts—produced a single cell of a new hybrid yeast species among billions, maybe trillions, of other cells. From just this one cell, the new species came to dominate. “Because it’s a superior descendent of the mixture, it will eventually take over the culture,” says Faria-Oliveira.
Knowing lager yeast’s parents let Verstrepen run genetic tests to find the deepest roots in its family tree. The data took him to the early 1600s, and he could see with confidence that lager yeast’s Saccharomyces cerevisiae parent had German weissbier lineage.
While the tests revealed no clues about the Saccharomyces eubayanus parent, Verstrepen now had three very useful pieces of information: two known parents, a precise window of time (1602–1615), and a location where this hybridization had to have happened (a Bavarian brewery).
The challenge, then, was to discover where in Bavaria a weissbier ale yeast might have crossed with a cold-tolerant eubayanus strain. Researchers needed to overlay the scientific data with beer history to find the precise moment of lager yeast’s inception.
Taking Verstrepen’s data and analyzing it alongside Munich’s beer history, Dr. Mathias Hutzler, from the Technical University of Munich’s Research Centre for Brewing and Food Quality, came to a new hypothesis: Lager yeast was born when Saccharomyces cerevisiae was introduced into a brewing environment where Saccharomyces eubayanus was already present. In other words: A weissbier yeast was introduced into a brewery where lagered beer was brewed.
It turns out there was only one place where this could’ve happened. But before we get there, you need to know a few key facts:
When what’s now known as the Reinheitsgebot—the Beer Purity Law—was signed by the Duke of Bavaria in 1516, it ruled that Bavarian beer could only be brewed with barley, and not wheat. Weissbier, which was mostly made with wheat, was therefore banned, and that made lagered beer—then known as braunbier—the sole beer of Bavaria.
The Bavarian royal family, the Wittelsbachs, had built themselves a braunbier brewery in Munich’s Alter Hof Palace in 1589, partly to save money from all the beer they were importing. That reveals a deeper concern: They were broke.
And as for wheat being banned? There was actually one exception: In 1548, the Duke of Degenburg was given exclusive rights to brew weissbier to compete with imported wheat beer from Bohemia. He died without an heir in 1602, so those rights defaulted to the Wittelsbachs.
By 1602, nearly a century after its near-total ban, weissbier wasn’t a popular type of beer in Bavaria. But the Wittelsbachs were in debt, and weissbier had significant advantages: It was quick to produce and could be brewed year-round, unlike lagered beers. Moreover, the family had a monopoly on its production, and they could force taverns to buy it.
So the Wittelsbachs hired Degenberg’s weissbier brewmaster and, as was customary at the time, he brought his yeast with him to Munich. Weissbier was then exclusively brewed in the royal brewery, and made alongside braunbier, from 1602 until 1606 or 1607, when a new weissbier brewery was built nearby to keep up with the demand. (That building housed a brewery until 1895, when it was transformed into the Hofbräuhaus.)
In 2023, Hutzler co-authored a paper suggesting that lager yeast was born during this brief historical moment, when Munich’s royal brewery produced both braunbier and weissbier.
The exact mechanics or moment of conception aren’t known, but we have clues: As braunbier could only be made during the cooler months, its yeast had to be revived at the beginning of each brewing season, and weissbier yeast would have helped that process, creating a higher-stress environment in which something like rare mating could occur. (Hutzler’s paper suggests a second possible event: A brewer from Einbeck, who made a strong weissbier that was very popular with the wealthier class in Munich, came to work for the royal brewery in 1614, and brought his yeast with him.)
Whichever the case, a single hybridization event created one new yeast cell. That yeast came to thrive, and then dominate, in the cold environment, gradually taking over the culture. As a prominent brewery, the Hofbräu would have shared its yeast with other local brewers, and it would have spread from there. Eventually, lager yeast would be used throughout Europe, and then the world. And the rest, as they say, is history.
Not quite so fast. There’s still one major missing piece to this mystery: Saccharomyces eubayanus has never been found in Germany, or in any neighboring region.
The yeast has been located in places as far-flung as Patagonia, Tibet, New Zealand, Wisconsin, and Dublin. The current theory is that wood or barrels made from Tibetan oak or walnut, which carried a culture of Saccharomyces eubayanus, ended up in a Bavarian brewery, but experts like Verstrepen question this. “Did some eubayanus really get lost on the Silk Road and make its way to Germany? I dunno. I believe there must have been a local population, but we cannot find it anymore.”
If we overlap science and history once again, we find two possible reasons for that missing piece. From 1300 to 1700, Europe went through several small ice ages, and those colder periods may have created a temporary environment in which the cold-loving Saccharomyces eubayanus could live. The second is that, during Germany’s recovery from World War II, many of its primary forests were felled. That may have made extinct Saccharomyces eubayanus’s natural home.
Today, Dr. Mathias Hutzler and others continue to search for the yeast. Finding Saccharomyces eubayanus may not teach us more about lager yeast today, given how much it has since evolved, but it will solve the final mystery of how the yeast species used to brew more than 90% of the world’s beer came into existence.
“If you find eubayanus in Germany or [the] Czech Republic, you are the hero,” says Hutzler.
As lager became more popular outside of Bavaria in the middle and late 19th century, lager yeast was sent to breweries throughout central and northern Europe, then North America. But that “yeast” was almost certainly still a stellhefen mixed culture, albeit one dominated by Saccharomyces pastorianus.
That didn’t change until 1883, when Emil Christian Hansen, laboratory director at Carlsberg in Copenhagen, found a way to isolate single-cell brewing yeasts, and then propagate them. His discovery forever changed brewing by enabling pure-culture fermentation.
Hansen’s discovery meant that, for the first time in history, lager beers were brewed with only Saccharomyces pastorianus. It demarcated a new era of lager brewing, and was the final stage in a centuries-long journey that took lager from a hearty brown beer brewed only in Bavaria to a crisp golden beer brewed everywhere in the world. That process was aided by growing industrialization, with new technologies including artificial refrigeration, pasteurization, filtration, large-scale bottling, and transportation helping make lagers the standardized bright, refreshingly dry, pale beers we know today.
As the 20th century wore on, new emphasis was placed on consistency. Lager became an industrial product brewed on an enormous scale, so it had to be made as efficiently as possible. Yeast was the major variable in brewing, influencing how long a beer took to ferment while also being the ingredient most likely to impart negative characteristics. Finding strains that were more efficient, and which made tasty beers, became vital to the industry.
This need gave rise to TUM34/70: the most widely used lager yeast strain in the world.
The person behind its development, Professor Ludwig Narziß, studied and worked at the Technical University of Munich, which shares its campus with the centuries-old Weihenstephan brewery. In his early work, he isolated dozens of commercial yeasts from breweries and tested their qualities. The 34th yeast he isolated performed best overall.
“He recognized that to find the right lager strain is the key to lager beer,” says Hutzler. The yeast was known as TUM34, and soon became the most trusted and reliable choice for Bavarian brewers, including the Weihenstephan brewery.
In 1970, Narziß re-isolated TUM34 from Weihenstephan, and that version became known as TUM34/70. The yeast was so good, and so reliable, that it became a standard lager yeast all around the world, with each major yeast supplier offering their own, brand-name version.
“We can’t say that it’s responsible for the most lager,” says Hutzler, accounting for how major global brands have their own house yeast strains. “But it’s inarguable that TUM34/70 is the lager yeast used by the most breweries.”
“Does it ferment quickly, reliably, does it flocculate at the end, does it reduce diacetyl, and does it taste good?” asks Jeremy Swainson, head brewer of Utopian Brewing in Devon, England. 34/70 answered yes to all of those questions. “It succeeded in its essential industrial performance,” he says.
Despite its industrial appeal, 34/70 is now used by numerous lager-centric craft breweries. “It’s our house yeast; we use it in everything,” says Lisa Allen, head brewer and owner of Heater Allen in McMinnville, Oregon. She describes it as a very versatile yeast. Heater Allen has used it to brew everything from pale and dark lagers to low-alcohol lagers—even pale ales and IPAs.
“34/70 is as good as you can get to counting on something that is natural and will do what it wants anyway,” says Will Loring, co-founder of Lesser-Known Beer Co. in Winston-Salem, North Carolina. “It can be boring, but I still think that’s a positive. That’s what you want in a lager yeast.”
Is it boring or is it just reliable? The underlying narrative of lager’s history is that brewers were trying to make their beer taste good as consistently as possible. Storing it in cold cellars softened rough edges and nullified bacteria. Later, pure-culture fermentations enabled predictability, and filtration and pasteurization ensured stability. Lager’s story is a 500-year-long tale of slow, patient refinement. Then, 34/70 made it even more reliable.
But the utilitarian nature of the yeast isn’t appealing to all brewers. That speaks to a modern shift in lager, and the desire to preserve the beer’s key drinking qualities while also seeking new nuances of flavor.
“34/70 is a fantastic yeast—it’s just one we don’t use,” says John Lenzini, co-founder and technical director of Schilling Beer Company in Littleton, New Hampshire. He explains that the yeast is “almost so neutral [as] to be non-interesting,” and that Schilling has instead curated two Czech lager strains and two German lager strains for its beers, which he says have more character.
All the brewers I spoke to about 34/70 said the same thing: The yeast is good, it’s easy to access and easy to use, and they know what they’ll get from it. There are yeasts that produce more flavor or work faster or ferment more efficiently, and there are yeasts that give more character to beer, or make crisper lagers. But 34/70 is the great all-rounder.
“34/70 is as good as you can get to counting on something that is natural and will do what it wants anyway. It can be boring, but I still think that’s a positive. That’s what you want in a lager yeast. ”
It’s hard to sing the praises of something that’s so simple, but that’s the true significance of a yeast like 34/70: It made lager easier to make, and that meant more brewers could brew lager all around the world. Moreover, its simplicity meant people knew what to expect from it, and they trusted that.
Aside from the exact details of how Saccharomyces eubayanus arrived in a Bavarian brewery, many of the questions of lager yeast and lager production have now been “solved.” And yet, there is something unsatisfying in that neat conclusion. Lager is not a drink that stands still.
“I was very lucky to talk to [Narziß],” says Hutzler, “and he told me he had a little bit of bad conscience because, with his perfect optimization of the lager beer brewing process, he’s also a little bit responsible that a lot of the lager yeasts were skipped, and stellhefen lager strains were lost.”
Verstrepen echoes those sentiments—and then points to a new path forward. “Lager yeast is a cool story, but it’s also a bit sad because the genetic diversity of lager yeast is limited,” he says. “One of the things we can do, and we’ve done it in our lab, is we can make more lager yeasts.”
Verstrepen’s researchers have created around 50 of their own Saccharomyces pastorianus hybrids. “Some of them were horrible, but some of them were quite nice, and quite different from the ones we have,” says Verstrepen.
It’s happened elsewhere, too. There’s now a type of lager yeast, known as Renaissance—or by its brand name, NovaLager—developed by Lallemand Brewing in conjunction with Renaissance Bioscience in Vancouver, British Columbia. “Most lager strains are genetically very similar to one another,” says Eric Abbott, technical support manager at Lallemand Brewing. “There was a desire to produce a true lager strain that was genetically distinct and had unique performance characteristics from the existing lager strains on the market.”
By using non-GMO techniques, they created a “new strain which is three-quarters cerevisiae and one quarter eubayanus,” says Alexei Titov, Lallemand Brewing’s technical sales manager for Russia and the Baltics. That makes it distinct from all other commercial lager yeasts, which, like 34/70, are an even genetic mix of both parents.
“The higher composition of cerevisiae makes it more viable and more robust,” says Titov, adding that the yeast produces less diacetyl, doesn’t produce any hydrogen sulfide, and is more tolerant of higher temperatures in fermentation and maturation. Because of this, it can ferment warm and doesn’t need such a long maturation or lagering period, meaning brewers can make lagers more quickly, using less energy. Unlike the blank slate of 34/70, it also adds a very light red apple and tropical fruit ester profile. “It’s subtle, but you can feel the difference between this and a neutral lager strain,” Titov adds.
“Lager yeast is a cool story, but it’s also a bit sad because the genetic diversity of lager yeast is limited. One of the things we can do, and we’ve done it in our lab, is we can make more lager yeasts. ”
With efficiency and sustainability becoming a greater concern for breweries, and with flavor preferences side-stepping away from pure utilitarianism and toward more distinctive character, lager looks poised to change and evolve once again.
When I next return to the Hofbräuhaus, I order a mug of helles while I try to piece together this mystery, and why it matters.
At some point in time, a single yeast cell was born into a great vat of beer, one cell among billions of others. Somehow, that one cell now has its DNA in nine out of every 10 beers drunk in the world. That’s remarkable. These new details reveal something of that origin, but it still remains teasingly incomplete.
“Most lager strains are genetically very similar to one another. There was a desire to produce a true lager strain that was genetically distinct and had unique performance characteristics from the existing lager strains on the market.”
Lager’s evolution, on the other hand, did appear to be complete: It couldn’t get much lighter or drier or crisper or more global. And yet, lager continues to move forward. There are new ingredients, new processes, new flavor demands from drinkers, and now new yeasts to make them. Really, when we think about the history of lager, we’re talking about the history of brewers and scientists trying to understand how to get yeast to do what they want. At least now, with the latest hypothesis, the story leads us to one specific, and very important, place.
“It is an honor that one of the most common yeasts used for brewing originated in the Hofbräuhaus,” says Sebastian Utz, Hofbräu’s deputy technical director. The brewery continues to use TUM34/70, and would even if it didn’t play a role in the yeast’s birth. “After all, its fine aroma and fermentation characteristic, and its inner values, matter more than its origin. But can you think of a better birthplace?”
Words by Mark DredgeIllustrations by Colette Holston
