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Where lager came from: the genetic mystery of bottom-fermenting yeast

Lager is the most popular type of beer in the world, but few drinkers know that we owe its existence to one of the most fascinating genetic mysteries in the history of brewing. The bottom-fermenting yeast that gives lager its clean, cool character is not an ordinary strain, but a hybrid of two different species of yeast. What is more, one parent of this hybrid remained unknown for centuries - it was discovered only in 2011, and on the other side of the globe, in the forests of Patagonia. It is a tale of how a chance meeting of two species of yeast gave rise to a whole category of beer. In this post you will get to know the genetic mystery of the birth of lager, its wild ancestor and the reason it ferments cold. It is a journey into microbiology, which explains where lager came from. Let us start with how lager differs from ale.

Lager versus ale - the role of yeast

The world of beer is divided into two great families: lagers and ales, and the basis of this division is yeast. Ale is made thanks to top-fermenting yeast, which works at higher temperatures and gives a beer of a richer, often fruity and spicy profile. Lager is made thanks to bottom-fermenting yeast, which works at low temperatures, near zero, giving a beer that is clean, smooth and refreshing, without the fruity esters typical of ale. This difference in yeast and temperature of fermentation is the foundation of two completely different worlds of beer. Lager requires cool fermentation and long, cold maturation (lagering), hence its name. Bottom-fermenting yeast is the key to understanding lager, but its origin long remained a mystery. Where did yeast capable of working in such cold come from? The answer turned out to be one of the most beautiful mysteries of beer science. So let us get to know this remarkable yeast more closely.

Bottom-fermenting yeast

Lager yeast, that is bottom-fermenting yeast, bears the scientific name Saccharomyces pastorianus. Its most characteristic trait is the ability to ferment at low temperatures, at which ale yeast would freeze or work very poorly. It is this yeast that gives lager its clean, neutral profile, devoid of fruity and spicy notes. This yeast settles at the bottom of the fermentation vessel (hence the name bottom fermentation), unlike ale yeast, which gathers at the top. For a long time scientists knew that lager yeast was exceptional, but did not understand its origin. Only genetic research revealed the astonishing truth: Saccharomyces pastorianus is not a single species, but a hybrid - a cross of two different species of yeast. This discovery opened the door to solving the mystery of the birth of lager. The hybrid nature of this yeast explains its unique properties. So let us get to know both parents of this remarkable hybrid.

The mystery of the hybrid

Saccharomyces pastorianus, lager yeast, is a hybrid of two species: Saccharomyces cerevisiae and Saccharomyces eubayanus. The first of them, Saccharomyces cerevisiae, is a well-known species - the same yeast used to produce ale, bread and wine. The second, Saccharomyces eubayanus, is a cold-tolerant (cryotolerant) species, which is most likely the parent passing to the lager yeast its key ability: working at low temperatures. The hybrid thus combined the best of both worlds: the fermentative capacity of Saccharomyces cerevisiae with the cold tolerance of Saccharomyces eubayanus. This combination turned out to be ideal for brewing beer at low temperatures. The problem was that for a long time only one parent was known - cerevisiae. The other, eubayanus, was a phantom species: its genetic trace was seen in lager yeast, but the species itself was found nowhere. It was a real mystery, which intrigued scientists for years. Where was the mysterious second parent of lager hiding?

The discovery in Patagonia

The breakthrough came in 2011. The mysterious second parent of lager yeast, Saccharomyces eubayanus, was described for the first time - and in a surprising place, in northern Patagonia in Argentina. It was discovered in the forests of southern beech (Nothofagus), with which this species is ecologically associated, often in the company of sweet growths on the bark. Genome analysis confirmed the sensation: Saccharomyces eubayanus from Patagonia turned out to be about 99 percent genetically identical to the corresponding fragment of lager yeast. It was the missing link: the wild ancestor that had long been sought. The discovery solved the years-long mystery of the origin of lager. It turned out that the species that gave the world one of the most popular beers lived wild in the distant forests of South America. It is fascinating that the history of European lager leads all the way to Patagonia. The discovery of 2011 was a milestone in beer science. But it also posed new questions, because the mystery turned out to be deeper than thought.

How the cross happened

Since the wild ancestor of lager lived in Patagonia, how did its cross with European ale yeast happen? It is still a partly open question. It is known that lager yeast arose as a result of hybridisation, probably in the times when in Europe beer began to be brewed in cool cellars and caves, at low temperatures. There the wild eubayanus yeast, somehow arrived in Europe, met the ale yeast cerevisiae and combined into a hybrid perfectly adapted to cold fermentation. Interestingly, research suggests that hybridisation may have happened several times, in independent events, giving different lineages of lager yeast. The origin of the European eubayanus is still being studied, and some leads point beyond Patagonia itself. How exactly the wild species from South America reached European cellars remains the subject of research. The birth of lager is a tangle of chance, human activity and biology. This mystery is still not fully solved, which makes it even more fascinating. It is a tale whose last chapter is still being written.

Why lager ferments cold

The heart of the lager phenomenon is the ability of its yeast to ferment at low temperatures, and this is a direct legacy of the wild ancestor. Saccharomyces eubayanus is a cryotolerant species, that is cold-tolerant, capable of fermenting sugars such as glucose and maltose at reduced temperatures. After hybridisation Saccharomyces pastorianus combined the fermentative capacity of cerevisiae with the cold tolerance of eubayanus - perfect for beers brewed at low temperatures. It is precisely this resistance to cold that lets lager ferment slowly, near zero, which gives a clean, smooth profile without fruity esters. The low temperature slows the metabolism of the yeast and limits the formation of byproduct aroma compounds, hence the characteristic cleanliness of lager. Without the gene of cold tolerance, inherited from the wild Patagonian ancestor, lager would not exist in the form we know. The ability for cold fermentation is the gift of a wild species that changed brewing. We write more about the difference between lager and ale in our post on why lager is harder than ale.

The genetic mystery in a table

Let us set the elements of the lager puzzle side by side:

The table shows how lager arose from the combination of two species. Saccharomyces cerevisiae, known from ale, gave the fermentation capacity, and the wild Saccharomyces eubayanus from Patagonia the key cold tolerance. Their hybrid, Saccharomyces pastorianus, is the lager yeast that gave the world its most popular beer. The discovery of the wild ancestor in 2011 solved a years-long mystery. It is proof that behind a glass of lager hides a fascinating biological history, reaching all the way to the forests of South America.

Why it is worth knowing this story

Getting to know the genetic mystery of lager enriches the understanding of beer. First, it shows how huge an influence yeast has on beer - it is yeast, and not only malt and hops, that decides the division into lagers and ales. Second, the story of the discovery of the wild ancestor in Patagonia is a fascinating tale of how science solves mysteries that intrigued for centuries. Third, it makes you realise that even the most common beer in the world has a remarkable, biological history, reaching to distant forests. Fourth, it deepens respect for the microorganisms that, though invisible, shape the flavour of our favourite drinks. A conscious beer lover knows that behind the clean flavour of lager stands a chance cross of two species from centuries ago. Next time, drinking a lager, it is worth thinking of its wild ancestor from Patagonia. It is knowledge that turns a glass of ordinary beer into a window onto the fascinating world of biology. Lager is not only a drink, but also a living history of evolution.

The key points in a nutshell

Lager owes its existence to bottom-fermenting yeast, Saccharomyces pastorianus, which is a hybrid of two species: the ale-known Saccharomyces cerevisiae and the cold-tolerant Saccharomyces eubayanus. The hybrid combined the fermentation capacity of cerevisiae with the cold tolerance of eubayanus, which lets lager ferment at low temperatures and give a clean, smooth profile. For centuries the second parent remained unknown - it was discovered only in 2011 in the forests of Patagonia, where it turned out to be almost genetically identical to the lager ancestor. How exactly the cross happened in European cellars is still being studied. It is one of the most beautiful mysteries of beer science. Want to compare lagers and record your impressions? Keep tasting notes in the GustoNote app. See also our posts on the difference of lager versus ale and on why lager is harder.