Why Your Definition of a Lager is Probably Both Right AND Wrong

by Mark E. Lasbury for Indiana On Tap

You walk into your favorite beer bar and belly up to the rail. To your right, you hear one patron describe a beer to their friend, “It’s a lager, so it uses bottom-fermenting yeast.” Down on your left, the beertender helps a new craft beer fan, “Lagers are beers that use a different yeast and are held at low temperature for a good amount of time to make them clearer.” Finally, the beer list set before you is split between ales and lagers. The truth is, they’re all right, and they’re all wrong.

Lagering is really a technique, not a style of beer. The word comes from German word “lagern,” meaning cold storage. Technically, you can lager any beer, but lagers have come to mean only a few particular styles. Yes, there are more lagers than just your favorite pilsner or the prototypical macro-American lager, Budweiser. Kölschs are probably my favorite lagered beer, followed by bocks and doppelbocks. Ask me in July and I might mention marzens as nice lagers, but I had so many in the last Octoberfest season that I have still a hard time even saying the word marzen right now, let alone drinking another one.

Look at how crystal clear the Workingman’s pilsner from Fountain Square is. One of the reasons for this is the lagering process that precipitates so much more of the aggregates that cause chill haze. Photo credit: 1000 beers.com

In general, beers considered to be lagers use a lot of Pilsner malt, which might be why so many people associate pilsners with all lagers, although Vienna malts and Munich malts might be used as well. In America, lagers might also contain adjuncts, like rice or corn, as with the macrobeers. There is so much rice in Budweiser that I sometimes wonder if I shouldn’t use chopsticks to pick up the glass. But, in the technical sense, these are beers treated in a certain way, not defined so much by their ingredients.

Lagering Is About Temperature
So, if lagering is actually a process rather than a thing, what does it mean to lager a beer? Basically, it means holding beer at temperature just above freezing for an extended time. This results in a loss of chill haze; the low temperature precipitates many protein aggregates and molecules that tend to make beers less clear. This is a feature of pilsners and other light lagers, they tend to be crystal clear even when served too cold (as they often are).

But lagering isn’t all about looks either. There are chemical reactions going on in your beer as it ages – even as you drink it. Some are good; they add flavors and get rid of off flavors. On the other hand, some reactions are bad; the beer may oxidize or develop different off flavors.

One of the tenets of chemistry is that all most chemical reactions take place more slowly at lower temperatures. Luckily for beer, the bad reactions seem to be affected by cold storage (lagering) more than the good reactions are. So in total, lagering is a way to increase the good and decrease the bad in beer.

The idea that lagers all use bottom fermenting yeast is wrong for the simple reason that ales can be lagered as well. To prevent confusion, it is often said that ales are cold conditioned, but it’s really the same thing. True, ales often have flavors that might be lost with weeks or months of lagering (doppelbocks might be lagered for a year), so cold conditioning of ales is usually much shorter, but it serves basically the same purpose.

Underneath the new brewery /taproom for Blue Blood Brewing in Lincoln, is an old robbers cave that opens onto the river. They intend to use part of it for cold beer storage, and have tours in the rest. Photo credit: Matt Ryerson, Lincoln Journal Star

Bryan Suter, the head brewer at Books and Brews, sat down for a couple minutes to help me work out the terminology. He said that lagering usually denoted weeks rather than days for cold conditioning of ales, and that lagering can be done at slightly higher temperatures than the cold crash for clearing ales during a cold conditioning process. Blue Blood Brewing in Lincoln, Nebraska has a robber’s cave that they are using for aging and lagering (around) 55˚F and Christian Moerlein in Cincinnati has cellars in which they do their lagering. I recommend that you look into the story behind Cincinnati’s underground breweries in Over The Rhine – simply fascinating.

Lager Yeast Differences
Lager beers, if they use lager yeast (bottom fermenting yeast) are brewed a bit differently from top fermenting yeast beers. They might start fermentation at a slightly higher temperature to get the yeast going (metabolizing sugars to alcohols), but then they are almost always fermented at a low temperature, maybe 45-55˚F or even down to 45˚F with some strains of yeast. Because of the temperature effect on chemical reactions we alluded to above, this temperature means that the yeast ferment slowly, so this first fermentation needs to take place over a couple of weeks instead of a few days as it does with top fermenting yeasts.

The big difference here is that bottom-fermenting yeast can survive and thrive at lower temperatures than can top-fermenting yeasts, but they are all related. In fact, the thousands of years that beers were fermented at low temp.s with top fermenting yeast (S. cerevisiae or the South American/Tibetan/Wisconsin S. eubayanus) actually brought about the evolutionary development of S. pastorianus (the so-called lager yeast). Each time they fermented at low temperature, a certain umber of mutated yeast cells, those that had some genetic change that allowed them to work at lower temperatures, grew better than the other yeast, and became a larger portion of the total yeast population. Research from 2012 showed that S. pastorianus is actually a hybrid of S. cerevisiae and S. eubayanus; it has all the chromosomes of both the parent strains. Hence, now some yeast strains work much better on top and at higher temperature, while S. pastorianus works at low temp.s and on the bottom.

Ale yeast sit on top and ferment at a higher temp. The opposite is true for lager yeast. Of course, we now know that none of these terms applies 100% of the time. Image credit: Popular Science

In truth, the top/bottom distinction makes no difference to the beer at all, but there have developed some differences between the two strains that actually make a difference to the final product. The cold fermenting yeast (lager) tends to eat more kinds of sugars (referred to as higher attenuation). Sugars that might remain in ales, like more complex or differently joined sugars, are metabolized by lager yeast, so beers made this way tend to be less sweet, less fruity (bottom fermenting yeast produce fewer fruity esters), and slightly higher in alcohol.

Diacetyl Can Be A Difference
In addition, beers made with ale yeast are fermented at higher temperatures, so they don’t require one step that lagers need, and this is another reason Bryan thought that the terms lagering and cold conditioning diverged. One product of fermentation is called diacetyl, the same compound that movie theaters use to add butter flavor to popcorn. In most beer, this is not a good thing. Diacetyl is produced by yeast when they eat sugars, but after other sugars are used up, yeast will take in diacetyl and metabolize it as well. For lower temperatures, the metabolism is slower, so for lagered beers that use bottom-fermenting yeast, there is a 2-3 day period called a diacetyl rest, where the temperature is raised to about 62˚F. This period of time allows the yeast to eat up the diacetyl and rive off a bit of the excess CO2 that can lead to other off flavors.

The diacetyl rest is necessary for lager yeast beers because of the low temperature fermentation, and because S. pastorianus tends to produce more diacetyl and sulphur compounds. These need to be gotten rid of before the lagering step (cold storage), so the rise in temperature allows for faster metabolism of diacetyl and volatilization (evaporation) of the sulphur.

Diacetyl is produced by yeast when it breaks down sugars. However, leave the yeast in longer and they will take diacetyl back up and convert it to compounds that have no taste. But, remember, some people like the buttery taste of diacetyl – like the Czechs and their pilsners. Image credit: https://sites.google.com/site/gatesdiacetyl/origins

Conclusion – There Are Hybrids
So… that’s it, lagers might use a different yeast, but that doesn’t mean they can’t be treated in most respects like ales. Ales might have a different yeast, but many/most are treated to a lagering step (as with kolschs), even if it is shorter and called cold conditioning.

In support of this middle ground are the unfiltered kellerbiers, and the complete destruction of the lager/ale dichotomous key (has to be one or the other). These hybrid beers use bottom fermenting yeast (kellerbiers) at a higher than normal temperature or top-fermenting yeast at a lower than normal temperature. You probably know another bottom-fermenting hybrid – the California Common, or steam beer or California common; it ferments with lager yeast at 60˚F or higher. In addition, baltic porters use lager yeasts at higher temperatures while traditional English porters use ale yeasts at slightly lower than normal temperatures – confusion reigns. On the other end of the scale, altbiers, kolschs, and cream ales use top-fermenting yeasts at very low temperatures in order to keep the ester formation down. Kolschs and alts often use a specific kolsch yeast that lives somewhere between bottom- and top-fermenters.

With all this being said, I can’t really offer any advice on whether or not to use the terms lager and ale. Hey, I never said I had the final word on this or even had an idea of how to develop a clear definition. All I know is that when when Walter and I hear people describing lagers vs. ales in a brewery or bar, we stay out of it.


Walter’s words of wisdom – Outdoor summer craft beer festivals can really benefit by the addition of oscillating fans for the attendees and brewers.


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