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Beer Science: The Genealogy of Lager Yeast

I am currently team-teaching a course on the Microbiology of Brewing Beer at Erie Community College as part of its Brewing Science and Service Certification program. A recent lesson topic on yeast biology and genetics led me down the rabbit hole of the origins of lager yeast. I became so intrigued by this topic, that I’ve been digging even further. I thought I’d share some of my findings.

Advances in modern technology have allowed researchers the ability to accomplish a world-wide screen of yeast species, obtained from diverse habitats and climates. Researchers capture yeast in the wild and then transport them back to the laboratory for sequencing of the genetic material residing in the chromosomes.

Long story short- researchers have hypothesized that the original lager strain is native to either South America or Asia. And as more genetic data is accumulated, it’s very possible that others will make similar claims.

But before we get to those results, let’s review the brewing properties of ale and lager yeast.

Ale vs. Lager Yeast

The yeast used in brewing today come in two broad categories: ale and lager. The main difference between ale and lager yeast is the temperature at which the yeast are able to ferment sugars in wort (the precursor of beer minus the alcohol). Here’s a picture of where a brewer might find an ale and a lager yeast in a fermentation vessel and the different types of beer made using each yeast.

LagerVAle
Differences between ale (left) and lager (right) yeast. (photo from Harbison, 2013)

Ale yeast are also known as “top cropping yeast” because they settle on the top of the fermentation vessel. Lager yeast are also known as “bottom cropping” yeast because they ferment on the bottom of the fermentation vessel. Ale yeast are used to produce the majority of beers in breweries today, for many reasons.

First, ale yeast are much faster at fermenting. Lager yeast can be harvested, or cropped, from the bottom of the fermentation vessel, whereas ale yeast are cropped from the top of the vessel. Lager yeast can take months to finish fermentation. Time in a brewery is of utmost importance, whereby the object is to create vast amounts of beer in a short time span. Beer that sits in a fermentation vessel takes up space and time. And time is, of course, money. This is one reason why breweries use ale yeast for most beer production.

Some of the basic differences between lager and ale yeast are shown in the table below:

Ale Vs. Yeast

 Ancient Yeast: A Brief History

Yeast has been used for many centuries. In fact, hieroglyphics suggest that yeast was used by Egyptians to produce alcoholic beverages and leaven bread over 5,000 years ago. In fact, Dogfish Head’s Ta Henket was brewed as an homage to these ancient Egyptians, and fermented with yeast obtained from Cairo.

Ta_Henket_bannerr_0

But keep in mind that Egyptians knew nothing about microscopy and yeast cells. Fast-forward a few thousand years. Starting in 1837, scientists helped elucidate the role of yeast in brewing. Some of the major advances in the discovery and advancement of lager yeast science were:

  • 1820-1830: Bavarian brewer Gabriel Sedlmayr was working at his family’s Spaten brewery in Munich. He isolated and perfected a cold fermenting yeast: a “bottom-fermenting” yeast used to make “lager bier”. It’s believed that this was the first iteration of what is now considered lager yeast. JC Jacobsen of Carlsberg brewery took this yeast home with him to Coperhagen

Spaten

  • 1837: Theodore Schwann proved yeast was alive, called it “Zuckerpils” (sugar fungus)

Schwann

  • 1838: Julius Meyen “Latinized” the name and changed it to Saccharomyces.

 

  • 1850-1870: Louis Pasteur proved scientifically that yeast was responsible for alcohol production in wine and beer.

Pasteur

  • 1880: Emil Christian Hansen discovered that brewing yeast was actually a mixture of several different strains, and is 1908 he called one particular strain Saccharomyces carlsbergiensis. More on this strain later.

Carlsberg

Modern Day Yeast

S. carlsbergiensis is not accepted as a species name any longer. That yeast species is now called S. pastorianus, named after Louis Pastuer. The reason for this is that it was discovered that these two yeast were genetically the same. The two species names should be treated as synonymous.

Of the 1500 or so species of yeast, only about 300 of these are species that can ferment sugar. However, very few of these 300 are able to produce reliable concentrations of alcohol. Because alcohol is toxic to cells, yeast will die as they ferment and the concentration of alcohol increases. Only a handful of strains have been discovered that can sustain alcohol concentrations of greater than 8%. Below is a table showing the alcohol tolerance of different yeast.

Alcohol Tolerance

So the question is: what is so different in these species of yeast? The answer, of course, resides in the genetic makeup of the yeast.

Genetics of Lager Yeast

Yeast possess very interesting and complicated genetics. Two species can exchange genetic material and make a genetic “hybrid”. Yeast can share, swap, duplicate or lose entire chunks of genetic material. Sometimes one strain ends up donating large stretches of DNA to another species, thus making a hybrid strain. Researchers have proven that the origins of lager yeast most certainly involve genetic mixing of strains.

Advances in DNA sequencing technology have allowed rapid accumulation of modern yeast strain data. It’s now possible to analyze and compare DNA from ale and lager strains. Here’s the going theory:

Lager yeast seem to be a genetic mix (or hybrid) of three different strains: S. cerevisiae, S. uvarum and S. bayanus. S. cerevisiae may seem familiar, because this is ale yeast. What this means is that ale yeast mixed with the original lager progenitor, presumably due to contamination and mixing of species in the brewery. Here is a figure showing what might have happened with the yeast strains in order to create a lager yeast.

the-difference-between-a-lager-and-an-ale
From Libkind et al., 2011. PNAS.

Notice that there are events hypothesized to take place in natural environments and brewing environments. S. eubayanus and S. uvarum, from nature, have contributed DNA to modern-day lager strains. SUL1 is a sulfate transporter gene that controls sulfate intermediate compound concentrations in the cell. The take-home message of this figure is that the current lager strain used in breweries is most likely a hybrid of ale yeast with contributions from other yeast.

The Origins of Lager Yeast

So we know that lager yeast are a genetic hybrid of ale yeast and some other “lager progenitor” yeast. Researchers have sampled and sequenced yeast from across the globe in an attempt to locate the original lager yeast. There are two locations hypothesized to be the birthplace of the original lager ancestor: Patagonia and Tibet.

Patagonia lager yeast was isolated from beech trees in the forest and results were reported in 2011. This Patagonia yeast species is called S. eubayanus, or “true bayanus”. Below is a picture of the galls that contain this yeast.

Patagonia yeast gall
Patagonian yeast can be found living in these galls. (photo by Diego Libkind)

And in 2014, Chinese researchers claim that the original lager yeast resided in Tibetan forests.

It’s difficult to imagine how exactly Patagonian or Tibetan yeast made it to Bavarian brewing vessels. It’s quite possible that there are more wild and as-of-yet undiscovered species living in Europe or elsewhere. Finding and identifying wild yeast in Europe would eliminate the need to invoke a means of intercontinental sea voyage for lager yeast.

Summary

The genealogy of lager yeast is an interesting story. Modern day lager yeast is a hybrid of many different yeast species, including the ale yeast S.cerevisiae. Current data suggest that lager yeast may have originated in Patagonia or Tibet. Over the years lager yeast have been artificially selected to ferment at lower temperatures and create a crisp beer.

 

References:

Popsci Article, Harbison, 2013
Lager Yeast presentation: Patagonia
Univ. of Wisconsin, Science Daily, 2011
Tibetan Yeast
Libkind et al., PNAS article, 2011

About Buffalo Beer Biochemist

Buffalo Beer Biochemist

Born and raised in Western New York. Ph.D. in Biochemistry. Professor of Microbiology and Chemistry. And lover of beer.

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