Pressurized Fermentations
In the world of beer, time spent in the fermenter and energy spent keeping things cold is money — making lagers particularly expensive to age. After all, we all know that lagering takes 40-plus days at near-freezing temperatures to make true and proper crystal-clear Pilsners and the like.
You can imagine, then, that commercial breweries have every incentive to cut the amount of time and energy needed to make a beer. Brewing profit margins are slim when you’re at the scale of beer pricing wars, so any penny saved is a penny back into the company coffers. It’s that expediency that has driven much of the research in lager processes and ingredients. From time to time, you’ll see news announcements about lager breakthroughs — new yeast strains that require less chilling, ceramic plates infused with stabilized yeast that can, in theory, ferment a lager lickety split. And if you’ve been paying attention to the homebrew gear market, you may be able to guess where we’re going with this: Pressurized fermentation.
One of the best things about homebrewing is that we sit at a swirling nexus of possibilities. Each of us can choose from a thousand ways of brewing and various levels of “tradition” vs. “technology” and this split is perfectly represented by the technique of pressure fermentation.
Here’s the basic theory: Warmer fermentations create more flavor compounds and in turn require more time to mellow. It’s a well understood fact that pressure during fermentation reduces ester formation regardless of the temperature. With fewer esters (and other flavor compounds) being produced, there’s less cleanup work needed.
We see this in the big tanks used by commercial brewers, and hence the reason we always caution that if a pro brewer says they ferment at 72 °F (22 °C), homebrewers should usually knock off a couple of degrees to adjust for the fact that our 5-gallon (19-L) columns of liquid just don’t have the same resulting pressure suppression that even a 200-gallon (760-L) batch self-generates.
Pressure fermentation takes that character suppression a step further. Rather than depend on the native pressure generated by our batch sizes and fermenter geometry, why not turn to a long-lived piece of brewing equipment — the spunding valve? You know it’s good for brewing because its name has a German origin (from spund in German meaning “bung” — aka how you’d seal a barrel of beer).
Unlike an actual hard bung, the spunding valve is a selectable pressure relief valve (PRV). You select a specific pressure (say, 14–15 PSI) and the valve allows that much pressure to build inside your vessel before venting to avoid over pressuring. These valves are widely used in commercial brewing, particularly at the tail end of fermentation (more on that later).
It wasn’t that long ago that if you wanted a spunding valve for home use, you had to build one for yourself. (Drew still has a homemade one full of automotive parts and enough Teflon tape to plumb a house sitting in his brewing toolbox.) These days you can buy any number of fermenter-specific or generic valves from homebrew suppliers. They have decidedly less Teflon tape!
When combined with an appropriate fermentation vessel, the spunding valve means you now have a pressure environment in your brewery in addition to your kegs. Let’s be very clear about that appropriate bit. By and large, general plastic vessels and all glass carboys are not appropriate vessels.
We’re going to repeat that for the folks goofing off by the fermenters in the back — don’t pressurize containers that aren’t meant to hold pressure. We have very few hard-set rules, but that’s a good one to have. No one needs to lose an eye because they’re making beer.
Don’t be fooled by the materials either — a good number of stainless-steel vessels are not meant to be pressurized. We both use Grainfather GF30 Conicals in the brewhouse; despite being lovely gleaming stainless steel, they are designed to release their lid if the pressure inside gets above ~3-5 PSI (this is to prevent the device from becoming an accidental 30-L pipe bomb).
There are other conicals and even plastic fermentation systems that allow you, with accessories and care, to pressurize your fermenter. Each system works a little differently, but the basic rules are the same. We’ve both used Corny kegs to do our pressure tests.
So, let’s determine how you want to “pressure ferment.”
The most common use of pressure fermentation is to cap the vessel towards the end of fermentation to capture CO2 and begin carbonating the beer naturally.
• Choose a target gravity to begin capping. Usually when you have about 4–8 gravity points (1–2 °P) left in fermentation. For instance, if you have a beer you expect to finish at 1.010 SG, you’ll want to cap between 1.014–1.018.
• Attach the spunding valve to your fermenter as directed (in our case, it was as simple as attaching the spunding valve on a keg gas fitting and plugging on the gas post).
• Dial in your specific desired pressure (14–18 PSI is common for carbonation).
• Let the beer finish and transfer under pressure to a waiting keg.
• Check the carbonation and serve when ready.
For the full-on pressure fermentation with the beer always operating under pressure, the process is much the same — except you attach the spunding valve from the start and go from there.
A few rules of thumb:
• What pressure and what temperature you use in fermenting is going to be largely strain-dependent. Some yeast strains produce solid and reliable results while others are much less effective working under serious pressure. Any of the 34/70 family of strains appear to perform like the global workhorse they are proclaimed to be. Drew has also used SafLager S-189 with positive results (a good place to start is around 13–15 PSI). There are several strains sold as “pressure fermenters,” but you can achieve the same results with trial and error with regular yeast strains. Keep in mind that until you gain experience with this technique, you’re bound to make mistakes, have things stall out, etc. It’s all part of the deal.
• Fermenting under pressure is a more stressful environment for yeast. More stress means you’ll need very healthy and viable yeast in solution to pull this off.
• While pressurized fermentations do produce (particularly with lager yeasts) a far less pronounced bit of kräusen, you’ll want to avoid fouling the spunding valve. Watch your pressures and use a system that has a secondary pressure escape.
• Because the beer will be naturally carbonated, you’ll need to take care to transfer the beer under pressure to preserve the carbonation.
• Dry hopping becomes trickier because beer geysers tend to happen when you introduce fine little bits of hop matter to a carbonated liquid. Many of the same folks who sell pressure fermentation systems also sell various pressurized dry hopping rigs (popular with the hazy IPA crowd to reduce oxygen introduction). You could transfer onto the hops under pressure to keep the mess down. Skipping those, if you’re fast you can probably pull it off, or be safe and degas the beer before introducing the hops.
• If you’re going for speed, you’ll want finings to speed up your beer’s polishing. Drew does this by racking into a keg with Biofine Clear and a shortened dip tube. (Floating dip tubes are another option for you dedicated gear heads!)
All told, when done right, a standard lager beer of reasonable gravity (~1.050) can be produced in two weeks at “ale temperature” (around 65 °F/148 °C).
Which brings us to the other point: When and why should you do this? And when should you not?
For us, pressure fermentation is an interesting technique, but one with little application to our preferred brews. Denny makes West Coast IPAs and Belgian ales, neither of which need/favor pressure techniques. Drew makes milds, cream ales, and saisons, and only one of those (cream ales) possibly benefits from pressure fermentation. The other two will lead him to talking your ears off about the value of open fermentation.
To us, capping to start naturally carbonating is a no brainer if you use pressurizable fermenters. It’s standard practice and wonderfully economical.
Full pressure fermentation makes the most sense if you either have the desire to quickly turn around clean, yeast-neutral lagers or you want to produce them while fermenting at more achievable fermentation temperatures. There are additional benefits around LODO (low dissolved oxygen) practices and avoiding hop oxidation as well, but we’ve talked before about the mismatch on technique to goals for our general practices.
The other reason to do it? Because you want to. You want to play around with the seemingly impossible trick of pulling off a lager without lagering. You want other shiny toys to play with. Or maybe you just want to make a beer in an indecently short amount of time. Nothing wrong with any of those, but for us, it’s a nice technique to have in the brewing tool chest, but not our usual way of fermenting. As with all things brewing, be mindful of why you’re doing the things you’re doing and what goals you hope to achieve!
