If there’s one comforting thing about the internet, it’s the warm familiarity of what are often endlessly repeated discussions on the same topics! One of the most common, at least in homebrewing circles, is this: “What pressure should I use to carbonate my finished and kegged beer?” The ensuing fusillade of recommendations tend to run towards some combination of “set it to X pressure for 48 hours, then reduce it to Y and serve it.” I have to say, that advice always irks me. Not because it’s wrong, per se — I’m sure you’ll get carbonated beer — but because it’s unnecessarily complicated. Instead, I tend to jump in and recommend a method that’s both simpler, requires no tinkering with the CO2 tank or regulator, and has the added benefit of ensuring smooth, easy pours: Just balance your draft system, once and forever. The steps are simple.
- Decide on a carbonation level and serving temperature, and identify the appropriate pressure to set your regulator to deliver (for reference, I recommend the Brewers Association Draught Beer Quality Manual, but you can find plenty of temperature-PSI tables online).
- Set your regulator and temperature controller to the appropriate pressure/temperature.
- Create enough corresponding resistance so that your beer is pouring at a manageable rate.
It’s Step 3 that most people need a little guidance on, and we’ll come back to it, but before we get there let me make the pitch for this overall simplistic approach.
The trouble with the “adjust the regulator” route, where you’re amping up pressure for a couple of days and then dropping it to “service” pressure, is that you’re inviting trouble into your life. Yes, you can shorten up your conditioning time, but you’re likely going to give back a lot of that time in the tinkering, irritating, nonstop “Dance of the Tweaked Regulator.” You’re coming down from your “pressurizing” PSI, and you either bleed the keg of gas or get a pitcher and let it blow out that first over-pressured gush of beer. Then you wait a couple of days to see if it’s at the right carbonation level. It’s too light, so you bump up the PSI. Now it’s pouring too fast. You cut it back. Now it’s pouring too slow. On and on it goes as you try to match your pressure to your desired carbonation level to your pour rate, and maybe you start playing with the temperature, too, and all the while you’re guessing at whether you need to make one more adjustment . . .
Instead, I prefer to just set it and forget it. Do the math on this once, and you’ll never need to do it again. When you have a new keg to put on, you just hook it up to the gas and wait. Simple.
Balancing The System
Balance starts in the keg. Whatever your desired carbonation level, there’s an equilibrium point where the pressure on the head space is exactly what it needs to be to not only create your desired CO2 level, but also to hold it there. If the pressure is too high, you’ll keep gradually pushing more CO2 into solution, slowly overcarbonating the beer. If it’s too low, you’ll gradually lose CO2 into the headspace, flattening the beer. Temperature matters here, too, because CO2 absorbs (or comes out) of your beer at different rates at different temperatures. So, we consult our handy PSI-Temperature table and find the required PSI. Let’s say we want to serve our beer at 39 °F/4 °C (a little cool, maybe, but it’ll warm up in the glass and this way you’re extending your flavor stability/shelf life). If we want 2.5 volumes of CO2, we find that we need right around 12 PSI (83 kPa) to create it and hold it at that carbonation level. Simple enough. Set your regulator, set your temperature controller, and hook up your keg.
Determining Carbonation: Volumes of CO2
That’s just the first two steps, though. Now we’re on to step three — balancing the system so that it pours properly. To do that, we need to create the right amount of resistance between the keg and the faucet (and, ultimately, your glass). Now, you can work this from the regulator side, but as noted previously, doing that requires some trial and error, with no guarantees you’ll find the right settings before you kick that keg! It has the added detriment of putting your beer in a state of flux. If you carbonate at high pressure but drop to 2–3 PSI (14–21 kPa) to serve at a lower pressure, you don’t have that equilibrium in the headspace, so your beer is slowly decarbonating and trending towards flat (or, really, pétillant). Likewise, if you carbonate at one pressure but, because you have too much resistance, you need to increase the pressure to address a slow-trickle of a beer pour (less common, but not unheard of if you’re pushing up from a basement kegerator or across a longer distance), you’ll end up with beer that’s slowly gaining carbonation and becoming more spritzy.
Instead, let’s balance that equilibrium pressure so that our beer stays at a constant carbonation level and pours smoothly. We have two tools at our disposal: Gravity and the beer line we’re pouring through. We have 12 pounds (83 kPa) of pressure pushing on the beer as it comes through the line. We need to create about 12 pounds (82 kPa) of resistance. Do that, and you get stable carbonation and a soft pour every time.
Let’s start with gravity. It’s not likely that you’re deliberately adding height to your pours by lowering kegs or raising taps, so this is most likely something you’re factoring in based on your draft system design rather than adjusting. All the same, it’s still important to do so! If your kegs are one foot (30 cm) below your taps, you’ll get about 0.43 pounds (3 kPa) of resistance. We back that off of our target “balance point” of 12 PSI (83 kPa), and we’re down to 11.57 pounds (80 kPa).
Most resistance will come from your tubing. The wider the tube and the smoother the surface, the less resistance you get. So, if we’re talking commercial “barrier” tubing, there’s very, very little resistance because it’s commonly used in long-draw systems where the beer is traveling as much as a couple of dozen feet before it reaches the kegs. Most of us, though, will use 3⁄16-inch ID vinyl tubing (common in home kegging applications), which creates roughly three pounds (21 kPa) of resistance per linear foot (0.3 m) [Note: this resistance number is not a hard rule, numbers vary depending on the tubing manufacturer. Be sure to check their numbers if available.] If we need 11.57 pounds (80 kPa) of resistance, we need 3.86 feet (or three feet, ten inches, or 1.18 m) of tubing between the keg’s out post and the faucet shank. Cut it, install it, and you’re done. You should, at the pressure and temperature we’ve selected (in this example), have perfectly smooth pours, at just the right carbonation.
Hook up your kegs, and leave them be. In 5-8 days, you’re pouring perfect beer!
What if you don’t have the time to give, though? It’s the night before the graduation party, and you have three kegs that you’ve just filled because (like most of us) you lost track of it and didn’t keg them last week when you should have.
This is where those high-pressure tricks come in handy. If you need carbonated beer in a hurry, start with leveraging pressure and temperature in your favor. If you have a temperature-controlled fermentation fridge, set your controller to 34 °F/1 °C and get that keg in there. Then, put your backup CO2 cylinder (you have one, right? If not, you can use your primary if it’s not too difficult to detach from your kegerator) in there with it, with the pressure turned up to 35 PSI (240 kPa). A couple of hours later, you should have cold, at-least-partially-carbonated beer – hook it up to your system, and let it take it the rest of the way up over time. This is also the method I use when I don’t have room in my kegerator for a finished keg, but might want it on hand as a backup for a party or event. Use this method to “pre-condition” a keg that you might need to put on at short notice. It’s a bigger pain to bring carbonation down than it is to tolerate it being a little low while it comes up, and even a short period of high-pressure/low-temperature carbonation will yield a reasonable amount of CO2 in solution, and you can still enjoy your homebrewed beer even if it’s not at its perfect carbonation level in the meantime.
Another time-honored method is agitation. If you’ve ever had a CO2 tank hooked up to your keg, you’ll notice that you hear the gas running into the keg — but only for a few seconds. At that point, it’ll go quiet. If you move the keg, though, you’ll hear the gas start to “run” again. Why the change? Because agitating the beer breaks the surface tension, you’re both increasing the surface area of the beer and the motion also “gulps” some of the gas in the headspace down into the beer. The result is quicker absorption of CO2 into the beer. Some homebrewers will set the keg on its side and rock the keg to get it to quickly “gulp” CO2.
Both of these methods come with a major caveat, though: They’re easy to screw up. I’m unaware of any particular formula or calculator that has reliably shown just how long to leave your beer on high pressure at low temperature to get a specific outcome — my approach to this is very much based on trial-and-error (about an hour at near-freezing and 35 PSI (240 kPa) of pressure, then onto my normal, balanced system). No one can tell you how, or how many times, or how long to shake your beer to get the “right” amount of carbonation. Far and away, the best method here is to plan ahead as best you can, and connect your kegs to a balanced system with at least a few days of time to let your beer get properly carbed.
Safe, Boring, Smart?
There’s one last element of this to touch on, and it’s this: Using this method, all of your beers will be served at the same carbonation level and temperature, regardless of style. Saison at the same pressure as usually-more-still Scottish ale. German Pilsner at cellar-temperature English pale ale. It’s true, you’re giving up some control over an important contributor to beer flavor. I still think it’s worth it, though.
First, most of your beers are going to be about the same pressure anyway. Yes, Berliner weisse should be jamming at three-point-something volumes, but it’s still pretty solid at 2.5. Yes, that ESB should be hand-pump sparkling, but it’s still fine at 2.2.
Second, you have other options. If you have a beer that’s spritzy and highly-carbonated, consider bottle-conditioning it instead of putting it on keg. If it’s meant to be only lightly-carbonated you can do the same, or put it on your draft system and bottle it all up right off of the faucet when it hits the just-right barely-there carbonation level.
Last, consider making a “high” and “low” settings chart for yourself, and adjust by temperature. If you want a more-carbonated set of beers, drop the temperature down to increase absorption. You’ll need to be careful about overcarbonation and the service problems it presents (since you’re forcing more CO2 into your beer than your system was designed to pour), but it’ll take time to get to that point. If you want it less-carbonated, increase the temperature. It’s not perfect, but it’ll work in a pinch, especially if it’s just for a few days to a couple of weeks.
And, of course, you can always use more than one regulator! Multi-body regulators allow homebrewers to hold kegs at varying pressure levels. Splitters and manifolds can be added along with a secondary regulator for more flexibility.
The relative advantages, though, of the safe, boring, set-and-forget method will usually be worth it. Make a good catch-all choice on carbonation levels, do the math (once) on pressure, temperature, and resistance, and enjoy your stress-free draft system and the freedom of not having to make constant adjustments or cleaning up after your Uncle Steve dumps head all over the place because your system is pouring a little too hard.
Just hook up your kegs and enjoy.