© 2022, Randy Mosher / Craft Beer & Brewing Magazine
Subtlety is the defining characteristic of lagers. Rather than the “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. It’s the unique characteristics of their yeast that sets 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 including DNA from another cold-tolerant yeast, S. uvarum with some from S. Cerevesia [[Ref: Sampaio, 2018]].
Compared to their wild cousins, brewing yeast has messy genomes, with between two and four copies of each gene and an irregular number of chromosomes. One researcher described S. pastorianus as “chimeric genomes composed of mosaics of the parental genomes [[Ref: Behr et al,. 2020]].
S. bayanus was recently discovered living on beech and other trees in its Patagonian home range. Another population was found in the Northern Hemisphere, with the notable exception of Europe [[Ref: Baker et al, 2019]]. Adaptation to cold by S. bayanus depends on mitochondrial DNA, apart from the main store of DNA in the cell’s nucleus. S. pastorianus has mitochondrial DNA from S. bayanus, enabling its cold-tolerant brewing properties.
Some think S. bayanus may have traveled from Western China by way of the Silk Road, but since the genetic material in S. pastorianus comes from an S. bayanus strain 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 theselikely lurked in the shadows until changes in Bavarian brewing practices opened an opportunity [[Ref: Peris et al., 2016]].
A 1553 edict in Bavaria restricted brewing to between St. Michael’s Day (Sept 29) and the feast of St. George (April 23), allowing cold-tolerant S. pastorianus to dominate. Interestingly, similar restrictions were common elsewhere in Northern Europe without lager yeast appearing.
Families and 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 thereafter represents an extreme bottleneck and virtually halted further evolution of lager strains [[Ref: de Vries et al., 2019]].
Used by Carlsberg in Denmark, Type 1 strains were also common in Bavaria and 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.
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 [[Ref: Monerawela et al., 2015]]. Later, in a still-unexplained process, much of the S. cerevesiae genetic material was deleted from the Type 1 progenitor while leaving the mitochondrial DNA—and its cold-tolerance—intact. Of the two, Type 1 is the better fermenter at cold (50 °F/10°C) temperatures, producing fewer esters and other aromatic chemicals, for a subtler beer. Because it doesn’t ferment the 3-unit sugar maltotriose, Type 1 beers may be as much as 20% less attenuated and noticeably sweeter than type 2.
Type 2 strains, on the other hand, ferment maltotriose completely, for a drier, crisper beer, suiting the taste of mass-market consumers. They’re also more estery that Type 1, sometimes adding a hint of apple (Budweiser) or banana (Coors).
A Bounty of Subtlety
At cool temperatures, lager strains produce less aroma than ale. This consists mainly of fruity compounds like higher alcohols and their corresponding esters. Here are the most important ones in lagers [[Ref: Urbina et al., 2020; goodscentscompany.com]] (my comments in parenthesis):
ethyl acetate > ethereal fruity sweet weedy green
ethyl hexanoate > sweet fruity pineapple waxy green banana (apple/anissed)
propan-1-ol > alcoholic fermented fusel musty
isobutanol > ethereal winey
‘active’ amyl alcohol > ethereal fusel alcoholic fatty greasy winey whiskey leathery cocoa
isoamyl alcohol > fusel alcoholic whiskey fruity banana
isoamyl acetate > sweet fruity banana solvent (banana candy)
2-phenylethanol > floral rose dried rose
2-phenylethyl acetate > floral rose sweet honey fruity tropical
ethyl proprionate > sweet fruity rum juicy grape pineapple
The production of these aroma compounds depends on a set of chemical reactions called the Ehrlich pathway, 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 [[Ref: Lin et al., 2022]]. Lager yeast also produces sulfur compounds, including H2s/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 fresh longer [[Ref: Xu et al., 2019]].
Ale yeast also produces the same esters as lager, plus others with higher molecular weights like 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 [[Ref: Urbina et al., 2020; goodscentscompany.com]]. At ale’s higher fermentation temperature, estery, floral and citrusy characters are far more dominant.
Lager or Just Lager-like?
Keep in mind that lager has two aspects: one, fermentation characteristics; and two, stylistic aspects such as recipes, gravity and attenuation. Getting the second part right will 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 a lot of brewers making delicious “near-lagers” fermented with ale yeasts, and there is some enthusiasm for the neutral “kveik” strains that can quickly make lager-like beers at cool room temperatures.
There are also beers that are intermediates: Kölsch and altbiers are considered öbergarige lagerbiers, or “top-fermenting lager beers,” plus steam beers that employ lager yeast at room temperatures. These are intermediate in terms of their aroma profiles. It’s actually somewhat difficult for inexperienced tasters to tell the difference between a “normal” lager and a cold-aged ale. At 5 Rabbit, 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 and Using
Choosing the perfect lager yeast can be a challenge. If you have extreme requirements—high-gravity worts, fast turnaround, large fermenters 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 and flocculation, you can find those to suit you. Beyond those, you really have to dig into the fine print of the manufacturers’ descriptions.
Often, strains are recommended for particular styles such as German or Czech Pilsner, Dortmunder, Oktoberfest and others. Hoppier styles generally benefit from more attenuative strains that enhance hoppiness. Darker beers need a less attenuative yeast, as residual sweetness harmonizes with their generally malty character. In terms of flavor, you’ll encounter terms like “malty finish, balanced aroma,” “clean, crisp,” “creamy, malty,” “dry and clean” and “apple fruitiness.” Not much to go on, but with other characteristics, it’s enough to make a choice. Hopefully.
While most of the lager strains on the market today are Type 2, there are Type 1 (Saaz) strains available, generally marked with “Bohemian,” “Budvar,” or other Czech identities. Proper temperature control is always crucial for lagers and 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 “Weihenstephan” strain known as TUM*34/70 is regarded as an exemplary Type 2 strain and is very widely used in commercial brewing worldwide [[Ref: Hutzler et al., 2019]].
*Technische Universität München, the home of the famous Weihenstephan brewing school outside of Munich.
Looking into the future, there is a lot of interest in new hybrids between S. cerevesae and S. bayanus as well as other cold-tolerant wild species such as S. kudriavzevii and S. jurei, recently isolated from ash trees in Upper Bavaria. These offer the possibility of unique, lager-like beers with enhanced or unique aroma profiles. In addition, 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 the beers brewed with them—on the shelves before too long [[Ref: Hutzler et al., 2021]].
References (In order of appearance)
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[[Ref: Sampaio, 2018]]
Microbiology (Reading). 2018 Sep; 164(9): 1069–1071.Published online 2018 Sep 3.
Microbe Profile: Saccharomyces eubayanus, the missing link to lager beer yeasts
José Paulo Sampaio*
doi: 10.1099/mic.0.000677 PMCID: PMC6230766 PMID: 30175956
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[[Ref: Behr et al,. 2020]]
PLOS ONE Published: September 23, 2020Research Article
Exploring the potential of comparative de novo transcriptomics to classify Saccharomyces brewing yeasts
Jürgen Behr, Meike Kliche, Andreas Geißler, Rudi F. Vogel
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[[Ref: Baker et al, 2019]]
Science Advances, Vol. 5, No. 130 Jan 2019
Mitochondrial DNA and temperature tolerance in lager yeasts
Emily Clare P. Baker, David Peris, Ryan V. Moriarty, Xueying C. Li, Justin C. Fay , and Chris Todd Hittinger
DOI: 10.1126/sciadv.aav1869
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[[Ref: Peris et al., 2016]]
PLOS Genetics Published: July 6, 2016
Complex Ancestries of Lager-Brewing Hybrids Were Shaped by Standing Variation in the Wild Yeast Saccharomyces eubayanus
David Peris, Quinn K. Langdon, Ryan V. Moriarty, Kayla Sylvester, Martin Bontrager, Guillaume Charron, Jean-Baptiste Leducq, Christian R. Landry, Diego Libkind, Chris Todd Hittinger
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[[Ref: de Vries et al., 2019]]
FEMS Yeast Research, Volume 19, Issue 7, November 2019, foz063,
Lager-brewing yeasts in the era of modern genetics
Arthur R Gorter de Vries, Jack T Pronk, Jean-Marc G Daran
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[[Ref: Monerawela et al., 2015]]
FEMS Yeast Research, Volume 15, Issue 2, March 2015, fou008,
Loss of lager specific genes and subtelomeric regions define two different Saccharomyces cerevisiae lineages for Saccharomyces pastorianus Group I and II strains
Chandre Monerawela, Tharappel C. James, Kenneth H. Wolfe, Ursula Bond
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[[Ref: Xu et al., 2019]]
J. Agric. Food Chem. 2020, 68, 2, 584–590Publication Date:October 17, 2019
Higher NADH Availability of Lager Yeast Increases the Flavor Stability of Beer
Xin Xu, Yumei Song, Liyun Guo, Wangqi Cheng, Chengtuo Niu, Jinjing Wang, Chunfeng Liu, Feiyun Zheng, Yu Zhou, Xingge Li, Yingjian Mu, and Qi Li*
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[[Ref: Urbina et al., 2020]]
Microorganisms 2020, 8(5), 755; Published: 18 May 2020\
Volatile Compound Screening Using HS-SPME-GC/MS on Saccharomyces eubayanus Strains under Low-Temperature Pilsner Wort Fermentation
by Kamila Urbina, Pablo Villarreal, Roberto F. Nespolo, Ricardo Salazar, Rocio Santander and Francisco A. Cubillos
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www.thegoodscentscompany.com
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[[Ref: Hutzler et al., 2019]]
Brewing Science 2019 Vol.72 No.3/4 pp.69-77
Resurrection of the lager strain Saccharomyces patorianus TUM 35
Author(s) : Hutzler, M.; Narziß, L.; Stretz, D.; Haslbeck, K.; Meier-Dörnberg, T. ; Walter, H.; Schäfer, M.; Zollo, T.; Jacob, F.; Michel, M.
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[[Ref: Hutzler et al., 2021]]
ORIGINAL RESEARCH articleFront. Microbiol., 31 March 2021
Unique Brewing-Relevant Properties of a Strain of Saccharomyces jurei Isolated From Ash (Fraxinus excelsior)
Mathias Hutzler1†, Maximilian Michel1†, Oliver Kunz1, Tiina Kuusisto2,3, Frederico Magalhães2, Kristoffer Krogerus2 and Brian Gibson4*
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New Since Article Publication
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[[Winans et al., 2020]]
Fermentation (MPDI) 6, 14, 20 January 2020
Saccharomyces arboricola and its hybrids’ propensity for sake production: interspecific hybrids reveal increased fermentation abilities and a mosiac metabolic profile
Matthew J. Winans, Yuki Yamamoto, Yuki Fujimora, Yuki Kusaba, Jennifer E. G. Gallagher and Hiroshi Kitagaki
doi:10.3390/fermentation6010014
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[[Winans et al., 2022]]
Fermentation (MPDI) 8, 87 18 February 2022Saccharomyces arboricola and its hybrids’ propensity for sake production: interspecific hybrids reveal increased fermentation abilities and a mosiac metabolic profile
Matthew J. Winans