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Cold, Healthy & Crowded: Lager Fermentation, Simplified

Even homebrewers who consistently ace their ales can get intimidated by the prospect of fermenting a lager. Here, Josh Weikert demystifies what makes it different and shares advice from some pros.

Josh Weikert Oct 11, 2021 - 13 min read

Cold, Healthy & Crowded: Lager Fermentation, Simplified Primary Image

Photo: Matt Graves/www.mgravesphoto.com

Despite many vigorous discussions about the best hop choice for hazy IPA (it’s Amarillo, by the way) and the right pressure settings for your kegerator (balance, set, and forget), the brewing conversation that draws me in more than any other often begins with a surprising degree of humility. It goes something like this: “I’m going to make my first lager. Any tips?”

Thinking back to my early days of homebrewing, I don’t recall lager being all that mysterious. Sure, we kicked around ideas for how to lager without proper temperature control, or how to make something very lager-like with ale yeast. But there was no secret about what made lager different: You ferment it colder.

With the benefits of hindsight and experience, we know it isn’t quite that simple—but as many distinguished brewers will tell you, it doesn’t have to be all that complicated, either.

The Yeast, and the Basics

When I reached out to ask some brewers, friends, and associates to weigh in on this topic, one of the best answers came from Matt Winans, research and development scientist at Imperial Yeast: “Lager yeast are like mules, the [offspring] of a horse and a donkey,” he says. They’re natural hybrids, and they “differ in brewing characteristics and traits just like the cousins differ in your family.”

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I’d never thought of them quite that way before, but it’s a handy analogy. Yes, the strains of “lager yeast” that we use are simply hybrid strains of a variety of parent yeasts that share a lot in common with our good friend Saccharomyces cerevisiae. We’ll discuss some specific strains—but for now, the salient point is that lager yeasts are simply a collection of yeast strains that share the common trait of being ideally functional at lower temperatures.

Start Cold

That’s our first core takeaway, in fact: Cold fermentation is good fermentation when it comes to lager yeast (at least initially). Scott Rudich, owner and brewmaster of Round Guys Brewing in Lansdale, Pennsylvania, has a simple fermentation plan for lager yeast: “Pitch at 50°F [10°C] and after three days, raise the fermentation temperature a couple of degrees per day.” After a while they just let it free rise to promote full attenuation, but that cool start is the key. Ryan Diehl, brewer and cofounder of Imprint Beer in Hatfield, Pennsylvania, has similar guidance: “We ferment cold, 50–52°F [10–11°C] but are quick to let it rise near the end of fermentation.”

One reason to do this: Some lager strains tend to produce more sulfur, and a more vigorous, late-kräusen fermentation period helps blow that sharp flavor well clear of your finished beer. Be cool—just not for too long.

Pitch Plenty

Besides temperature, we have the amount of yeast you’re using: You want to pitch enough cells to reduce yeast stress. A cooler fermentation is a slower fermentation, and sluggish yeast can throw off more compounds than they can sufficiently “clean up” without enough cells and a vigorous fermentation.

Jeremy Myers, head of production for Bachs Biermanufaktur in Saarland, Germany, cites this count as an essential part of a good lager fermentation: “High cell count and viability when pitching [are] critical.” Rudich agrees, recommending half-again as much yeast as you’d use for an ale fermentation of similar gravity. Diehl says that they “probably overpitch” at Imprint—but as a brewing “error” that’s basically in the same lane as saying you “work too hard” when a job interviewer asks about your biggest weakness.

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Pitch Healthy

All the brewers I contacted mentioned this point: Don’t just pitch a lot of yeast, but also make sure it’s healthy yeast. Jamil Zainasheff, “chief heretic” (owner and brewer) at Heretic Brewing in Fairfield, California, puts it this way: “You can’t expect good fermentation without healthy yeast, in the right quantities, with proper nutrition—just like you can’t expect kids to grow healthy and strong without proper nutrition.” Brewing up a good starter and giving your yeast sufficient oxygen and nutrients are great ways to get your fermentation off the ground and into orbit.

So, which of those points matters most? Tough call. “I don’t know if I’d say there’s one ‘important’ criterion for good lager fermentation,” Myers says, “as much as I’d say I believe there’s a few that are equally important.”

It’s worth noting that yeast are robust little animals: You can get away with some shortcomings if you’re careful in other areas. For example: I tend to pitch on the lower end of the volume scale, but I manage my temperatures and pay close attention to nutrition and yeast health, so I “get away” with it.

Short version? Control what you can, relax, and it should be fine.

Tips, Tricks & Tools of the Trade

Once you get past the basics, there are any number of approaches, additions, and modifications that will contribute to your lager-fermentation success. Some of this is technique, some is tools—and I’ve been surprised at how often brewers agree on these things. A lot of conventional wisdom and dogma fly around in brewing circles, but these aren’t your run-of-the-mill, overheard-at-brew-club kinds of popular ideas—yet I hear them from the mouths of multiple pro brewers.

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Harvesting Yeast for Re-Pitching

Jonathan Porter, owner and brewer at Smog City Brewing in Torrance, California, says the best advice he has about lager-yeast treatment is “definitely about timing.” He warns against waiting too long before putting that yeast back to work: “You can’t wait for a ton of yeast to settle out,” he says. “You have to watch viability daily, and as soon as you see a tiny drop, that’s when you need to re-pitch. Next time, you might even do it a day before!”

Others have more patience. “Harvesting two or three days after the beer reaches terminal gravity, before the cold crash, is the sweet spot,” says Eric Walp, head brewer at Doylestown Brewing in Doylestown, Pennsylvania. It may be counterintuitive, he says, but lager strains are sensitive to that cold crash.

They agree on this key principle, though: If you’re going to be working one batch into another on the same yeast pitch, don’t let your yeast get too sluggish and go dormant.

Feed Your Yeast

Nutrition is helpful to most yeast strains, but especially to lager yeast, which can begin producing detectable (and detestable) flavors if they lack a healthy environment. Yeast nutrient in the kettle, for example, is a boon to yeast health. Zainasheff at Heretic emphasizes zinc—typically added when pitching, or just before. A healthy dose of oxygen is a good idea, too.

Feed your yeast what they need, and they’ll reward you with a clean and complete fermentation.

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Consider Natural Carbonation

At Imprint, Diehl recommends spunding—the practice of placing a beer under its own pressure near the end of fermentation to naturally carbonate it. (A relatively simple DIY project is to create your own corny-keg spunding valve using a gas connector, a pressure gauge, and a pressure relief valve. For more on spunding, see “Gearhead: The Force Behind the Fizz,” beerandbrewing.com.)

“Our favorite thing with lagers is to naturally spund during the last quarter or so of fermentation and just finish the carbonation, if necessary, with head pressure,” Diehl says. “We try hard to not use a carb stone on lagers. This is something homebrewers who keg can easily do.”

Spunding is relatively rare in homebrewing circles, but not unheard of. However, this next suggestion had me feeling a bit anxious.

Try Open Fermentation

Bach’s Myers—who knows his way around a German brewhouse—told me this: “Don’t be afraid to ferment in an open fermentor with not only ale yeast, but lager yeast as well. We generally think of German brewers as very technical, practical, and pragmatic, and the first time I saw open lager fermentation in Germany it sort of blew my mind. [It is] not something I would have expected, but nonetheless, more common than you would think.”

Yes, that’s a safe bet. You can also bet that I’m absolutely going to try this. Tips on open fermentation at home: Instead of using an airlock, loosely cover your fermentor with a piece of sanitized foil and place it somewhere without drafts (such as the coolest corner of your basement or, ideally, a temperature-controlled lagering fridge). Replace the foil with an airlock as soon as primary fermentation is complete. Possible benefits include happier yeast and the “off-gassing” effect, as some undesirable compounds can escape more easily. (Also see “4 Reasons to Try Open Fermentation,” beerandbrewing.com.)

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Don’t Fear the Warmth

As for my own go-to advice, it’s simple: Don’t be afraid of relatively higher temperatures toward the end of a lager fermentation. Let the temperature rise gradually up to about 60°F (16°C) and the fermentation get as active as it can then. Anything that wasn’t crisp and clean already will have a much greater chance of being scrubbed or blown out if you allow the temperature to free rise. Lager yeast like it cold—but all yeast like it warm toward the end of the fermentation cycle.

Which Yeast?

If we agree generally on how to get the most out of lager yeasts, we most certainly do not agree on the best strains. Some like more traditional yeasts: At Heretic, Zainasheff digs Fermentis SafLager W-34/70, derived from a famous strain kept at Weihenstephan. He also warns against attempting a lager with fashionable kveik strains, which in his view, don’t brew convincing lager. “I have no problem with people brewing whatever they want, however they want,” Zainasheff says, “but for gosh sakes, let’s please stop calling them lagers. They don’t taste like lagers.”

At Round Guys, meanwhile, Rudich likes Fermentic SafLager S-23.

Bachs’ Myers, interestingly, suggests White Labs WLP001 California Ale, the Chico strain that has powered many American ales over the years. He says that fermenting cold with that yeast leaves behind a beer with just the kind of clean, crisp flavor we want in a lager.

At Imperial Yeast, Winans says their most popular lager strain is L13 Global, derived from Weihenstephan 34/70, which has “increased cold resistance, can’t use maltotriose, and has lower ester production.”

Whatever the tool for the job, and whatever the trick employed, the goal is the same: clean, complete fermentation.

Try, Try Again

Lager yeasts aren’t hard to work with; they’re just a little more temperamental. Don’t overthink it. Keep them cool, keep them healthy, crowd them in there, and you’ll come away with a lager that will make you proud—and then you get to do it all over again.

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