Subtlety is the defining characteristic of lagers. Compared to the more in-your-face personality of ales, lagers are suave and reserved. If ales are frisky puppies, lagers are purring cats. They’re not climbing up your legs; you have to meet them where they are. But lagers offer easy drinkability, a transparent showcase for brewing ingredients and sublime delights—beer after beer.
And it’s the unique characteristics of their yeast that set them apart.
Crazy Mixed-Up Yeast
Lager yeast, Saccharomyces pastorianus, is designated as a species apart from S. cerevesiae, or ale yeast. S. pastorianus is a cold-tolerant hybrid between ale yeast and a recently identified cold-tolerant species called S. bayanus—which is itself a hybrid that includes DNA from another cold-tolerant yeast, S. uvarum, with some from S. cerevisiae.
Compared to their wild cousins, brewing yeast have messy genomes, with an irregular number of chromosomes and from two to four copies of each gene. One researcher describes S. pastorianus as “chimeric genomes composed of mosaics of the parental genomes.” In short, they have evolved as a genetic hodge-podge.
In recent years, scientists have discovered S. bayanus living on beech and other trees in Patagonia. Another population was found in the Northern Hemisphere, though not in Europe. Whether S. bayanus adapts to cold depends on mitochondrial DNA, apart from the main store of DNA in the cell’s nucleus. Its more famous offspring, S. pastorianus, inherited that mitochondrial DNA from S. bayanus, enabling its cold-tolerant brewing properties.
One theory is that S. bayanus traveled to Europe from Western China by way of the Silk Road. However, since the genetic material in S. pastorianus comes from a strain of S. bayanus that was probably extinct before written history, this route was unnecessary. It could have been spread by migrating birds or other means. However it happened, one or more hybrids with S. cerevesiae occurred—and these likely lurked in the shadows until changes in Bavarian brewing practices opened an opportunity.
Famously, a 1553 edict in Bavaria required that brewing happen between St. Michael’s Day (September 29) and the feast of St. George (April 23). That helped cold-tolerant S. pastorianus to dominate. Interestingly, similar restrictions were common elsewhere in Northern Europe without lager yeast appearing.
Families & Functionality
Snuggled in its cellars, lager became immensely popular, spreading widely to Bohemia and far beyond. By the time lager yeast strains were isolated into pure cultures, there were at least two significantly different variants: Type 1, the so-called “Saaz” strain isolated by Emil Christian Hansen in 1883; and the Type 2 “Frohberg” strain isolated at Heineken in 1886 by Hartog Elion. This distinction persists to this day, but the rapid adoption of pure-culture yeast—as opposed to mixed—shortly after the identification of these types represents an extreme bottleneck. It virtually halted the further evolution of lager strains.
Used by Carlsberg in Denmark, Type 1 strains were also common in Bohemia (hence the name). Type 2 strains were used in Danish breweries other than Carlsberg and elsewhere, including Heineken. It’s not clear where it originated, but Type 2 is by far the prevalent lager strain today. (It includes the famous “Weihenstephan” strain known as TUM 34/70; the TUM stands for Technische Universität München, home of the famous Weihenstephan brewing school outside of Munich.)
The genomes of S. cerevesiae and S. bayanus collided in at least one hybridization event, resulting in roughly equal contributions from each parent species. There is also evidence that suggests separate hybridization events, with Type 2 having a stout-type yeast as its ale parent Later, in a still-unexplained process, Type 1 dropped much of the S. cerevesiae genetic material while leaving its mitochondrial DNA—and thus its cold-tolerance—intact.
The ongoing difference between these yeast types—and their differing performance when fermenting beer—is why the distinction matters. Of the two, Type 1 (the Saaz type) is the better fermenter at cold (50°F/10°C) temperatures, producing fewer esters and other aromatic chemicals, for a subtler beer. However, because it doesn’t ferment maltotriose (a trisaccharide, or three-unit sugar), Type 1 beers may be as much as 20 percent less attenuated and noticeably sweeter than Type 2 beers.
Type 2 strains, on the other hand, ferment maltotriose completely, for drier, crisper beers that suit the taste of mass-market consumers. They’re also more estery than Type 1, sometimes adding a hint of apple (Budweiser) or banana (Coors).
A Bounty of Subtlety
At cooler temperatures, lager strains produce less aroma than ale strains. This aroma consists mainly of fruity compounds such as higher alcohols and their corresponding esters. Via The Good Scents Company, which maintains an online database of aroma compounds, Chart 1 (above) shows the most important ones in lagers (with my comments in parentheses).
The production of these aroma compounds depends on a set of chemical reactions called the Ehrlich pathway; it’s a secondary metabolism of specific amino acids. To exploit that, brewers are experimenting with protease enzymes in the mash that liberate amino acids from proteins, enhancing particular activity in the Ehrlich pathway and enriching aromatics in the finished beer. Lager yeast also produces sulfur compounds, including H2S/hydrogen sulfide (rotten egg) and SO2/sulfite (burnt match). Both dissipate somewhat with lagering, but when present, sulfite can act as a preservative, keeping beer flavors fresher for longer.
Ale yeast produces the same esters that lager yeast does, plus others with higher molecular weights such as ethyl octanoate (fruity, winey, waxy, sweet, apricot, banana, brandy, pear) and ethyl decanoate (sweet, waxy, fruity, apple, grape, oily, brandy), as well as piney, citrusy terpenoids and many other compounds. At ale’s higher fermentation temperatures, these estery, floral, and citrusy characters are far more dominant.
Lager, or Merely Lager-Like?
So far, we’ve been talking only about yeast and how they behave. However, keep in mind that lager beer has at least two aspects: one, fermentation characteristics; and two, stylistic aspects such as recipes, gravity, and attenuation. Getting the second part right can put you close to the classics, but attaining both will get you all the way there.
The market is fairly forgiving. Drinkers focus on the obvious recipe characteristics, but a proper lager fermentation can bring that extra magic. That said, there are many brewers making delicious “near-lagers” fermented with ale yeasts, and there is growing enthusiasm for the neutral kveik strains that can quickly make lager-like beers at warm temperatures.
There are also beers that are intermediates: Kölsch and altbier are considered öbergarige lagerbiere, or “top-fermenting lager beers.” Steam beers, famously, employ lager yeast at ale-like temperatures, as do currently popular cold IPAs. These are intermediate in terms of their aroma profiles. It’s somewhat difficult for inexperienced tasters to tell the difference between a typical and a cold-aged ale. At 5 Rabbit Cervecería, we once switched from a neutral English ale strain aged three weeks to a lager aged six weeks. While we definitely could tell the difference, it was hard to characterize: maybe like a layer of gauze being removed, revealing what was underneath.
Choosing & Using
Choosing the perfect lager yeast can be a challenge. If you have extreme requirements—high-gravity worts, fast turnaround, large fermentors with massive hydrostatic pressure, super-malty styles—there are specific strains for those. If you’re looking for specific fermentation characteristics—sulfur production, temperature range, flocculation—you can find those to suit you. Beyond those, you really have to dig into the fine print of the labs’ descriptions.
Often, they recommend strains for particular styles such as German or Czech pilsner, Dortmunder, Oktoberfestbier, and others. Hoppier styles generally benefit from more attenuative strains that enhance hoppiness. Darker beers prosper with a less attenuative yeast, as residual sweetness harmonizes with their more malt-driven profile. In terms of flavor, you’ll encounter terms such as “malty finish, balanced aroma,” “clean, crisp,” “creamy, malty,” “dry and clean,” and “apple fruitiness.” Not much to go on, but with other characteristics, it may be enough to make a choice.
While most of the lager strains on the market today are Type 2 (Frohberg), there are Type 1 (Saaz) strains available, generally marked as “Bohemian,” “Budvar,” or other Czech identities. Proper temperature control is always crucial for lagers. This can be a challenge for homebrewers, but these strains demand cool fermentations and long, cold lagering to bring out their best. If you just can’t decide, the famous 34/70 is regarded as an exemplary Type 2 strain, widely used in commercial brewing around the world.
If we look into the future, there is a lot of interest in new hybrids between S. cerevesiae and S. bayanus as well as other cold-tolerant wild species such as S. kudriavzevii and 8S. jurei,* recently isolated from ash trees in Upper Bavaria. These offer the possibility of unique, lager-like beers with enhanced or unique aroma profiles. Plus, as it turns out, S. eubayanus and others also can brew pretty good beer on their own, so maybe you’ll start to see these more exotic yeasts—and beers brewed with them—on the shelves before too long.
Want to Dig Deeper?
Research into yeast genetics has accelerated in recent years; the ability to sequence genomes has shed new light on yeast evolution, challenged longstanding theories, and opened fascinating new lines of inquiry. Here are some academic articles to seek if you want to learn more.
“Complex ancestries of lager-brewing hybrids were shaped by standing variation in the wild yeast Saccharomyces eubayanus,” Peris et al., PLOS ONE, 2016.
“Exploring the potential of comparative de novo transcriptomics to classify Saccharomyces brewing yeasts,” Behr et al., PLOS ONE, 2020.
“Higher NADH availability of lager yeast increases the flavor stability of beer,” Xu et al., J. Agric. Food Chem., 2019.
“Lager-brewing yeasts in the era of modern genetics,” Gorter de Vries et al., FEMS Yeast Research, 2019.
“Loss of lager specific genes and subtelomeric regions define two different Saccharomyces cerevisiae lineages for Saccharomyces pastorianus Group I and II strains,” Monerawela et al., FEMS Yeast Research, 2015.
“Microbe Profile: Saccharomyces eubayanus, the missing link to lager beer yeasts,” José Paulo Sampaio, Microbiology (Reading), 2018.
“Mitochondrial DNA and temperature tolerance in lager yeasts,” Baker et al., Science Advances, 2019.
“Resurrection of the lager strain Saccharomyces pastorianus TUM 35,” Hutzler et al., Brewing Science, 2019.
“Unique brewing-relevant properties of a strain of Saccharomyces jurei isolated from ash (Fraxinus excelsior),” Hutzler et al., Frontiers in Microbiology, 2021.
“Volatile compound screening using HS-SPME-GC/MS on Saccharomyces eubayanus strains under low-temperature pilsner wort fermentation,” Urbina et al., Microorganisms, 2020.