When you keg your beer some wonderful advantages become apparent. First and foremost, carbonation is generally much easier to dial in to your taste or to a certain style guidelines. Made possible by the regulator and physics you can literally dial in the level of carbonation that you want. The normal “set it and forget it” carbonation method is generally fool proof and takes about 7-10 days in my experience. But can it be done faster? What if you brew a beer for a party but your fermentation took longer than anticipated? Or what if you run out of beer and but you have a completed carboy of beer waiting on deck for that next empty keg? There is a way to get there faster. Its call the rapid force carbonation method, or the high pressure shake method.
When planning to force carbonate by any method its always best to have the beer chilled first. There is no way around that part of the deal. Cold beer absorbs CO2 better than warm beer. So plan for at least overnight, or the better part of a day to get the beer as cold as your serving temp at least.
In short to rapid carbonate a beer all you have to do is put the beer under pressure that’s 2-2.5X higher than your intended serving pressure, at cold temps and shake until done. But let me first say, its real easy to overshoot your preferred carbonation level so go at it in stages and taste as you go. OK disclaimer over, lets carb!
Hook up your gas line and purge that beer really well. The purging is super critical because rapid force carbonation requires that the beer get shaken around to expose as much of the beer’s volume to the head space of CO2. If the O2 isn’t all the way out of there the shaking will increase the rate of oxidation as well as carbonation… Not good.
Once the gas line is hooked up and keg purged (burped) you can dial up the pressure to 20-30PSI. I tend to like 20-22PSI. You can go to 30PSI but the process will go faster and you may over-carbonate. Next you simply hold onto one of the keg handles and shake it for 5 minutes. You’ll actually hear the gas flowing through the regulator if you are next to it. After 5 minutes I like to let the beer rest for 15 minutes. When I return, I’ll shake again and rest. After 3 cycles of that I’ll go ahead and draw a sample and taste it for carbonation.
At this point there should be noticable carbonation. Decide from there whether you want to shake for 3 more cycles or 1 one more cycle. Rest then taste again. I prefer to start slowing down to one round of shake and wait at this point and taste as I go. With practice you can do a pretty good job of gauging how close you are getting to your target and shake accordingly. Maybe only shaking for a minute each cycle as you think you are getting close.
Viola carbonated beer.
Now for the down sides. Some research tends to indicate that beer foam and foam stability is a one time deal. Meaning that when foam forms some small amount of foam stabilizing proteins are used up and will never contribute to foam again. When you shake the beer, even under pressure, some of those foam positive compounds may be getting used up. So if you have to shake quite a bit, you might be killing the ability to make foam. This research isn’t fully understood, nor have I really dived into the biochemistry of it. I will say from experience I think I get better foam and head from a pale ale that I slowly carbed vs. rapidly carbed. Your milage may vary.
Second down side. If you try and do this on a beer that has been uncarbonated but is still flat in the keg the shaking process will stir up any debris that had settled out of the beer. I have set beers aside for cold conditioning in the keg and forgotten to carb them in the process. I have drawn off a sample of crystal clear (but flat beer) only to be forced to pour well carbonated and cloudy beer because I needed to serve the beer for an event in a short timeline from rapid force carbonation. So if you want to carbonate flat, chilled and cleared beer; I recommend that you rack the flat beer to a new keg first if possible. Essentially, you are using the first get as a bright beer tank!
Lastly, be warned for the third or forth time… its easy to over carb. And letting the carbonation out is a slow process no matter what method you use. And be absolutely sure you have no O2 in there before you start shaking that beer up.
Good luck with rapid force carbonation.
BREW ON!
