Your Lager Can Take the Pressure

Brewers, I’ve found, are stubborn people. Tell one they can’t do something, and, as Marcus Aurelius said, “the obstacle becomes the way.”

Many moons ago, a fellow brewer told me I could ferment lagers warmer if I put them under pressure—but they also said, “It’s like microwaving a steak—it will cook, but it won’t taste right.”

That sounded familiar. I’d heard that very analogy used to describe direct additions of lactic acid to Berliner weisse—exactly what I’d done to mine, and it won Best of Show. So, I decided to add “pressurized fermentation” to my list of brewing dogmas to test.

Guess what? It turned out great. Pressurized fermentation is not only a viable way to produce high-quality beers—especially lagers—more quickly, but it has a host of benefits that make it worth the slight cost and effort.

Here, we’ll dig into the myriad benefits of pressurized fermentation, some of the science behind why it works, what to watch out for, what equipment you’ll need to do it, and, of course, how.

Why Pressure Ferment?

The most common reason given to ferment beers under pressure? Speed.

“We do all of our lagers in this manner,” says John Stemler, head of brewing operations at Chatty Monks in West Reading, Pennsylvania. “It allows us to produce lagers at light speed.”

Yet speed is only one of the many reasons you should consider this method. It’s also cleaner, gets you more beer for your effort, reduces the risk of oxidation and some off-flavors, and gives you more control over your finished beer.

But first things first: It really is very fast.

I tend to brew small, both in strength and in volume—my typical batch is about 5.2 percent ABV and 3.5 gallons (or about 13 liters). This allows me to get more variety, develop recipes quickly, and test more new ideas because, quite simply, I’m brewing faster and more often. Pressurized fermentation feeds directly into this mentality because it’s quicker and because it allows for warmer fermentation at lower risk.

Technically, you could achieve the same outcome—that is, brewing lots of lagers—by having more kegs and lots of cold storage space. But that’s costly in money as well as time. Pressure fermentation, meanwhile, also gives us a head start on carbonation—even more time saved.

Time isn’t the only benefit, though. Pressurized fermentation is also cleaner—figuratively, if not literally (more about hop explosions later). Under pressure, yeast produce less of the things we don’t want in most lagers and many ales, such as esters, diacetyl, and fusel alcohols. The method can also mean fewer vessel transfers and lower risk of oxidation, thus improving flavor stability and helping us avoid dulling and off-flavors. Some argue it also leads to better retention of volatile hop aromas (though I haven’t noted that, personally). In any case, a cleaner beer is more likely to showcase that hop character. Potentially, you’ll also get more beer: Pressurized fermentations produce less kräusen, so you can fill your vessels up higher without worrying about fouling your valves.

Here’s the real attraction for me, though: It’s one more thing that increases control. Beer can be flakey, as we all know from experience, and yeast especially so. Anything that increases my level of control over their environment—and does so in a way that lets me dial in what I get out of them—is a winner in my book.

The Science of Pressurized Fermentation

Why does pressurized fermentation work like it does? The short version: Pressure and carbon dioxide change how yeast behave.

Yeast produce different flavor compounds under different conditions, and the pressure in a pressurized fermentation can influence the types and amounts of flavor compounds produced. The most significant difference is the production of esters. We’ve already noted that temperature equals speed in fermentation: Warmer yeast are more active, and they metabolize the sugars in their environment more quickly. However, warmer temperatures also encourage yeast to kick off more esters, especially as the amount of ethanol in the beer inevitably increases. So, how does pressure come into the picture?

First: Pressure, as a physical force, reduces yeast metabolism in ways that inhibit the metabolic processes that produce ester compounds. Pressure makes it harder for yeast to absorb and express certain nutrients, but it does not prevent their conversion of sugars to ethanol and CO₂. Essentially, we get the benefits of limited esterification without sacrificing yeast’s primary conversion function—though we do give up some viability and growth, as we’ll discuss later.

The reduced availability of oxygen also limits ester production. In a nonpressurized fermentor, the yeast have more access to atmospheric oxygen. But in our pressurized fermentor—which has higher concentrations of CO₂ in both the headspace and dissolved into the beer itself—there is less oxygen available to the yeast. That leads to lower levels of ester production. Notably, CO₂ also increases the acidity of the environment, and the lower pH level also inhibits ester production.

Esters aren’t the only thing inhibited—it’s also possible that diacetyl is impeded. Pressurized fermentation at warmer temperatures can result in a faster, more complete fermentation process, allowing the yeast to consume more of the diacetyl produced during fermentation—after all, we’re moving quickly into “diacetyl rest” temperatures. In addition, the pressure can help to suppress the formation of diacetyl in the first place by promoting a more efficient conversion of diacetyl precursors into other flavor compounds. I’ll note, however, that scientific studies are not unanimous on the relationship between pressure and diacetyl. My read on these results is that they are variable by yeast strain, so your mileage may vary.

This leads me to an important caveat: The impact of pressure on ester production, diacetyl, attenuation, and more can vary depending on the specific yeast strain being used and the fermentation conditions employed. Some yeast strains may still produce notable levels of esters in a pressurized environment while others may produce almost none. We can and should tinker with various parameters such as pressure, temperature, pitch rate, batch size, and more to get the flavor profiles we want.

The good news: With faster turnaround on your batches, you can dial in these variables more quickly.

Equipment and Process

Converting to a pressure fermentation system requires surprisingly little equipment—and you probably already have a lot of it. It also won’t change your process all that much.

All we need is a vessel that can hold pressure—no glass carboys!—a valve to regulate said pressure (which you can easily build yourself), and some pressure and temperature management (which isn’t much different from what you’re probably already doing).

First, the vessels. For homebrewers, the simplest answer here is a standard five-gallon (19 l) corny keg. This has the benefit of being widely available and more than capable of handling the pressure. In fermentation, we’ll rarely venture above 20 psi, max, so keep that figure in mind when shopping around. There are specialized, purpose-built fermentors that can do the job here, too. But if you already have a spare corny or two, you’re good to go.

Next, you’ll need an adjustable pressure-relief valve (or APRV) to regulate the pressure in the vessel and “hold” it where you want it. If you bought a pressure-capable fermentation vessel, this may have been included—but if you go the corny-keg route, you can use a spunding valve that attaches to your gas post. These valves are reasonably priced, but this also represents a very approachable and cost-effective DIY project; you already have lots of the component parts in your keg/draft equipment junk drawer (we all have those, right?). If you really want to have some fun with corny-based fermentation, you can also investigate floating dip tubes so you can ferment, condition, and serve all in the same vessel. (For more about that, see No (Car)boys Allowed.)

The process is straightforward. Just transfer your wort into a pressure-capable vessel and pitch your yeast when you’re at a proper temperature—i.e., anywhere in their usual preferred fermentation range. Next, set your APRV or spunding valve to your target pressure. As a rule of thumb, start most strains at 10 to 12 psi; I end up at 14 psi for most beers. You can dial that up or down based on your results, but you’ll probably never go much higher than 17 to 20 psi.

Matt Winans, research and development scientist at Imperial Yeast, says they’ve had successful lager fermentations at or below 1 bar (14.5 psi). He recommends the popular 34/70 lager yeast—Imperial’s strain of it is L13 Global—because “it keeps good vitality and viability under pressure, and [it] maintains the great fermentation profile it’s known for.”

There’s some debate about whether to put your wort under pressure right from the start by hooking it up to forced CO₂. I’ve reached a healthy compromise: For an ale, I let pressure build up naturally, which allows some ester production. For lagers, however, I give the pressure the head start.

Temperature can start relatively high. I start my pressurized lagers at 58°F (14°C), then leave them at room temperature after 48 hours. The ales are at room temperature the whole time; in summer I might hold them under temperature control at a balmy 68–69°F (20–21°C), but the whole point is to drive the fermentation forward—so, don’t be afraid unless you’re going well above 70°F (21°C).

Just bear in mind that you may need more pressure to get your “clean” beer as temperatures increase. Fermentation will likely be done in a week or two—even for lagers—and then you can ease off the pressure and reduce the temperature. Or, you can jump straight into conditioning and preserve all that nice, free CO₂ already in solution.

Best Practices

Pressure fermenting reduces some concerns, but that doesn’t mean we have nothing to worry about. There are unique considerations that come to bear, including yeast selection, attenuation, clarity, and (this is fun) dry hopping.

Yeast

First, not all yeast strains will be a perfect fit for this method, though most will work well.

“Any yeast will have suppressed ester formation if you put it at 1 bar,” or about 15 psi, says John Stemler at Chatty Monks. “This was confirmed by a contact I have at a large brewing-yeast laboratory. Pressure fermentation–specific lager strains are only sold because it makes some people more comfortable.”

That’s not to say that all strains are equally productive under pressure, but don’t feel that you must use a “pressure-specific” variety. As I often say: Try, then trust. As a jumping-off point, varieties of the 34/70 lager strain work beautifully here. I’ve also been told—and, anecdotally, it’s been true for me—that dried yeasts work particularly well in pressure ferments compared to liquid yeasts.

Attenuation

Pressure inhibits yeast-cell growth and viability, so attenuation is a concern. We can address this by producing a more fermentable wort. Mashing at optimum alpha-amylase temperatures (150–152°F/66–67°C) and for longer (75 to 90 minutes) can help.

Stemler also says that some strains might benefit from a mid-ferment nutrient addition, but also that it’s not usually necessary for him. At Imperial Yeast, meanwhile, Winans recommends a few practices meant to make life easier on the yeast.

“First and foremost, keep a good pitch rate,” he says. “Pressure suppresses cell growth and acts as a stressor to yeast cells, so try to keep the other yeast stressors to a minimum, especially your OG—keep your gravities to a moderate level. I like to start at around 1.050, 1.060, or so.”

Clarity

Using pressure to brew lager more quickly means that you don’t get a key benefit of patience: a clearer beer.

“One downside is you have to be more aggressive with your clarification techniques since you don’t have all that lager time to drop bright,” Stemler says.

Although your beer will drop clear eventually, to really take advantage of the time savings, you’ll want to leverage some of the more effective finings and/or choose a higher-flocculating yeast. (I’ve found that two rounds of gelatin do the job just fine.)

Dry Hops

Maybe my favorite concern (for sheer entertainment value) is dry hopping during a pressurized fermentation. While amusing on video, however, a hop volcano is not something any brewer really wants to see (or clean) in person.

Thanks to the many nucleation points on hops, dumping them in can cause a lot of CO₂ to release—and if you don’t get your lid back on pronto, you could end up covered in sludgy green foam that only briefly smells wonderful. You could also end up with a big mess on your hands (and face, and floor, and clothes, and …).

You have two choices here: Ease off the pressure and temperature over a few days, then add; or act quickly and roll the dice. At home, I’ve found that I can slam in hops and get the corny lid resealed in time—but if you’re working with a screw-on pressure lid and a plastic vessel, you may be in for a wild ride.

To keep safe, consider a few tips from the pros:

• De-pressurize the vessel before dry hopping.
• Don’t stand directly over the opening (or port) when adding hops.
• Add hops slowly instead of all at once.

Pressure Is a Privilege

Fermenting under pressure isn’t something you should necessarily do as a beginner, but you could. It’s an industrial practice that can be miniaturized—and if it works for commercial breweries trying to free up tanks more quickly, then why not for a homebrewer trying to save time or squeeze in more brews?

Anything that gets us brewing more, and more often, is a win, and pressurized fermentation is a fantastic way to get more out of your system without sacrificing quality. After all, more pressure doesn’t have to mean more stress.