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Keg Force Carbing Methods Illustrated

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Bobby_M

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If you rely on a bottle of CO2 gas for carbing your kegged beer, there are basically two ways to go about it; set and forget and what I'll call "burst carbing". Some folks talk about this second method as "force carbing" but it's all done with force so forget it. For example sake, let's assume you want to carb your 45ºF beer to 2 volumes of CO2....

Set and forget relies on certain gas laws that will determine the carbonation level based on pressure and temperature. The volumes of carbonation will eventually reach an equilibrium to the head space pressure that is applied (what the regulator is set to). You'd use the charts like this one http://www.kegerators.com/carbonation-table.php to figure out what that pressure needs to be. In our example, the chart shows it would take 9 psi to reach 2 volumes in your 45ºF beer.

The second method, burst carbonation, uses a much higher initial pressure and even some gas diffusion techniques like shaking or airstones to encourage a quicker solution of the gas. In our example, you might put 30psi on initially. If you refer back to the chart, you'll see this pressure, if left long enough will equilibrate to 3.79 volumes given enough time. The trick/difficulty in this method is knowing how long to leave it at the elevated pressure to get close to your desired volumes without overcarbing.

Some people understand pictures better than words so I drew this.



The green line is the set and forget method. You can see that it will take about 2 weeks to reach your desired volumes. Some folks will argue that they have carbonation in 1 week but "some" carbonation is not exactly equilibrated carb level though you might enjoy it anyway. I'm not 100% sure how long it takes but I have noted an increased carb level between week 1 and 2 on more than a few batches so I'm calling it 2 weeks to get it pretty close. You'll notice a small increase from week 2 to 3 but it's slight.

The blue line is just an example of a well executed boost carb. You'd leave it at approximately 3 times the equilibrium pressure for 24 hours, then drop it down and purge the keg so the headspace is now at the "chart pressure". If you do it right, you'll get close and then it will only take a couple more days to reach your desired volumes.

Highlighted for emphasis: More often than not, people in a hurry will try boosting even more by going with higher pressures and/or shaking the heck out of the keg. This usually results in what the red line is showing. You overshoot the carb level and then fight with the keg for several days to get it back down by purging the pressure a few times.

The final point I want to make is that the only reason I'd advocate a boost carb is when your beer has already aged/conditioned prior to making it to your kegerator and you need the beer to be drinkable in less than two weeks (poor planning on your part of course). I noted on the chart that if you went from primary right to keg at week zero, no matter how fast you carb, it will still take at least 3 weeks to taste decent. Therefore, why boost carb at all?
 

the_bird

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Good info and nice presentation, although I think I'd fall into the camp of "carbonation is pretty much there" by the end of week 1. I would think the green line would have more of an upward curvature between T=1 and T=1week. I have a hard time believing that the amount of carbonation increases at a linear rate for those two weeks, rather than having a shape more like the blue line (what's the term I'm looking for - logrhythmic?) albeit with less curvature.
 

findthefish

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Yeah it seems like there's been a lot of these types of questions lately. Now hopefully people actually see this before posting.
 
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The problem is that lots of people just don't want to take the time to read up before asking. For Example: How many threads are there on weather or not you need to carbonate Apfelwein? Like 30?
 
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Bobby_M

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I should probably disclaim a bit. The drawing is not based on any hard data and I agree that the rate of carbonation for any of the methods could be different. It was meant to illustrate some very high level points. The green line probably should have been a bit more steep, probably closer to 1 volume at 4 days or so.

I know for sure that in my experience there's a very noticeable difference in carb level between week 1 and 2 though I admit that I can't guess a carb level with any accuracy just by looking and tasting. I believe it's easy to mistake carb levels by how much head forms during the pour (which is obviously not directly tied). What I think happens at the one week mark is you'll pull a pint, taste it, and decide that it's carbed to your liking. You'll ignore the fact that the pressure you set it to has the beer destined for 2.5 volumes and it currently stands at 1.9 volumes. Maybe you prefer 1.9 volumes on this beer. Over the next week, you have a pint here and there and noticing incremental increases of .2 volumes isn't going to happen. My 2 cents anyway.
 

Chriso

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The final point I want to make is that the only reason I'd advocate a boost carb is when your beer has already aged/conditioned prior to making it to your kegerator and you need the beer to be drinkable in less than two weeks (poor planning on your part of course). I noted on the chart that if you went from primary right to keg at week zero, no matter how fast you carb, it will still take at least 3 weeks to taste decent. Therefore, why boost carb at all?
Can you clarify a little on this point? Currently my procedure is to keg my beer after a 3-week primary. I seal the lid, then I consult Beersmith to see what PSI I should apply to carbonate at room temp, usually 65-70F. I set my reg to that pressure, apply the CO2 for about 15 seconds (until I can't hear the regulator groaning any more), remove the QD, and put into storage.

Am I essentially just sealing the lid, and not accomplishing carb? The last one I tapped after doing it this way was pretty nearly flat, and had to carb-over-time in the kegerator. After about 3 days it was acceptable, and very nicely carbed after a week.
 

the_bird

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If you're just hitting it with gas for fifteen seconds, yeah, you're not carbing the beer by any appreciable amount. The gas has got to stay hooked up for the gas to get absorbed. Any carbonation that you DID have when you first tapped it was probably mostly left over from fermentation.

If you're going to put the kegs in storage for a while after kegging but before serving, why not prime in the keg? Use a little corn sugar and save on a little CO2.
 

brown_dog_us

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Can you clarify a little on this point? Currently my procedure is to keg my beer after a 3-week primary. I seal the lid, then I consult Beersmith to see what PSI I should apply to carbonate at room temp, usually 65-70F. I set my reg to that pressure, apply the CO2 for about 15 seconds (until I can't hear the regulator groaning any more), remove the QD, and put into storage.

Am I essentially just sealing the lid, and not accomplishing carb? The last one I tapped after doing it this way was pretty nearly flat, and had to carb-over-time in the kegerator. After about 3 days it was acceptable, and very nicely carbed after a week.

Chriso,

I often keg my beer and then set it a side waiting for a spot in my beer fridge. I like to use 30 psi and a little shaking then I let it sit. When I'm ready to serve it, I put it in the fridge and hook up the lines with my normal pressure. In the time it takes for the keg to cool (24hrs) the beer is generally carbonated corrrectly or real close. I'm basically using the force carbonation method to get it close, but still low and then finishing the carbonation in the fridge.

I hope this helps,

Doug
 

Chriso

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I did for my first handful of kegs, and just ran out of dextrose for a couple weeks. Got more now.

Isn't 30 PSI still 30 PSI though, as far as the burst carbing method is concerned? Or are you implying to attach it to a constant 30PSI while warm, e.g. dedicate the tank to that keg until carbed? I guess the Correct Burst Carb line in the graph confused me, or gave me the wrong idea. Sorry to show my noobness, I'm still learning the kegging ropes.
 

brown_dog_us

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If you put your keg under 10 psi it will slowly draw more co2 from your tank into the keg. Eventually (a week or two) the beer will absorb all of the co2 it can at 10 psi. If you keep it at 30 psi and it absorbs all the co2 it can absorb you will have a way over carbed beer. You can force carbonate by "forcing" more co2 into the beer. This can be done by 30 psi for a couple days and hoping you back off to your normal pressure before you over carbonate or by using 30 psi and shaking the keg until the you don't hear the regulator making any noise. Bobby was talking about the first method. I like to do an abreviated version of the shake method when I don't have room in the beer fridge.

Doug
 

BierMuncher

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...Or are you implying to attach it to a constant 30PSI while warm, e.g. dedicate the tank to that keg until carbed?...
I haven't read many success stories for carbing kegs with CO2 at room temperature. Liquid absorbs CO2 much more readily at colder (basically serving) temps.

All my kegs age now for at least 2 weeks at room temp...following a three week stay in the fermenter/secondary. Then it's into the chiller and onto the gas at 30PSI for 48 hours. Kill gas. Bleed. Drop PSI to 10 and serve. (I'll drop that to 36 hours if the keg is already cold when I hook it up.

The warmer conditioning time is also important for another reason (spoken from experience):
Rushing from the fermenter to the cold keg will suspend yeast activity...not kill it...just suspend it. The beer may taste perfect while it's on tap and this isn't an issue if you're going to kill the keg. But if you decide to BMBF some of your beer into bottles to save for a later date...storing those bottles at room temp will re-awaken the yeast and they will convert the small amounts of residual sugars into CO2.

I'm still pulling bottles off the shelf that were perfect in the keg...that are now over carbonated. If you have any inclination to bottle off some beers from your keg...either age that beer warmer...longer, or plan to refrigerate those bottles immediately.
 
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Bobby_M

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I'm not sure if there's some magic math that can be done to figure out exactly how much of an initial pressure shot it would take at room temp to have a beer fully carbed without any additional constant gas. I've tried playing with the numbers but it made my head hurt so I gave up. If I understand it properly, you have to compare the headspace volume to the entire keg volume to know how the pressure will drop.

10psi? Heck no. That's 10psi in a headspace 1/10th the size of the whole keg. Once it absorbs into the beer, you get like 1 psi equilibrium which is .75 volumes. Let's try 40psi. 1/10th is 4 psi so room temp would be .9 volumes.... Hey, if it's a bitter, you might be close now.

If you're shooting for 2 volumes, it would take 20 psi equilibrium at room temp, which is about 200 psi in a 1/10th headspace.

Athough it doesn't get me all the way there, I still hit my kegs with 40psi before I tuck them into the basement for a short warm aging period (If I have enough supply flowing already of course). I'd rather start with .9 volumes when it hits the kegerator than 0 volumes.
 

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Athough it doesn't get me all the way there, I still hit my kegs with 40psi before I tuck them into the basement for a short warm aging period (If I have enough supply flowing already of course). I'd rather start with .9 volumes when it hits the kegerator than 0 volumes.
There! It makes sense now. Thanks so much for clarifying! I'm with it now... Seal and minimally carb, then chill and carb over a couple days before serving. That 3rd CO2 fitting in the kegerator is gonna own it's worth now :p.

Thanks!!!!
 

korndog

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kegging and carbing is a dance for sure. I came in .2 lower than planned on a couple of contest entries recently because i hadn't planned enough time using sit and forget method. I have had better luck blasting. Great chart and information. My dream setup now is to have separate regulators for all of my taps. I got one of these recently, which is a fairly useful item for some folks.

 

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Shameless bump, just because I had to dig and dig to find this thread, since I couldn't remember the name. Cheers!

(Should it be a sticky?)
 

WheeledGoat

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+1 on the sticky vote. It probably doesn't mean all that much to kegging vets, but this is a pretty valuable thread to new keggers. It's sure helped me out a bunch!!

Here's another page that helped me out a ton... plus on that page you can download the original Excel file of that chart at the beginning of this thread (much easier to read). I printed it out and stuck it in a sheet protector.
:mug:
 

madewithchicken

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About carbing at room temp, you should just use the chart. Usually about 30psi is right for me because I am aiming for about 2.5 vols.

Constant pressure is best. But if you only have 1 regulator you can just hit it with 30psi a couple of times a day.

There is the same amount of CO2 (2-3 volumes) dissolved in the beer as when it is cold. As long as you do not plan on dispensing it warm nothing important is different.

Dispensing warm beer is a different issue. It will have the same amount of CO2 when you pour it, but most is lost right away. Warm liquids have a hard time holding onto the dissolved CO2 when not under pressure. To prove this open a bottle of beer at room temp and another cold one. The cold one will stay bubbly longer. But when they were opened they had the same amount of CO2.

I carb at room temp because I have a coldplate in a mini fridge. One of my keg is always outside the fridge.

If I am worried about sediment I do not shake it. If it has been in a secondary for awhile and I am not worried about sediment I shake the keg. But as long as you don't up the pressure when you shake it you will not over carbonate it. This part is true for cold or warm beer.

I am sorry to sound like a know it all. But my high school chemistry teacher was a home brewer. We covered this.
 

holjim

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All my kegs age now for at least 2 weeks at room temp...following a three week stay in the fermenter/secondary. Then it's into the chiller and onto the gas at 30PSI for 48 hours. Kill gas. Bleed. Drop PSI to 10 and serve. (I'll drop that to 36 hours if the keg is already cold when I hook it up.
BierMuncher -- Do you mean that you'll rack to your keg (without sugar or gas) and let it sit for two weeks or do you shoot a bit of gas into it and then let it sit at room temp prior to chilling and force carbing?

Thanks!

Jim
 

BierMuncher

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BierMuncher -- Do you mean that you'll rack to your keg (without sugar or gas) and let it sit for two weeks or do you shoot a bit of gas into it and then let it sit at room temp prior to chilling and force carbing?

Thanks!

Jim
Just enough gas to purge the air out and get a good seal on the lid. I'll usually seat the lid with about 20PSI.
 

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Saw the sticky and just kegged my first two batches: apfelwein and an Anchor Steam clone.
 

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Ok So I attempted to follow Bobby M's instructions, but I'm still having some issues.

So I kegged last Saturday. The fridge is set to 38F. I let the kegs sit in the fridge for 4-5 hours before I connected any lines. I want 2.6 vol of carb.

I set the regulator to 37 PSI then shook the kegs for few mins then let them sit for 24 hours. Then I turned off the gas, released the excess pressure, turned the gas back on and set the regulator to 12.3 for the rest of the week.

Last night I turned the gas off, released the excess pressure, turned the gas back on and set the regulator to 5PSI for serve. From both kegs I poured 2 glasses and got 95% foam 5% beer, the beer was just slightly carbonated. So I turned the regulator back up to 12.3 and hear I am.

What am I doing wrong? Or am I just impatient? :confused:

Thanks,
 
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Bobby_M

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Ouch.. you're overcarbed. The burst carb thing in post #1 is described as leaving the keg on gas at 3x the chart pressure for 24 hours and not shaking the crap out of the keg first. The shaking process at that elevated pressure probably got you to the 2.5 volumes area and the additional 24 hours was icing on the cake. You're probably at 4 volumes now. You'll need to vent the keg a few times over a day's period. This can be accelerated by taking the keg out of the fridge.

Let's first talk about what kind of tubing you have between the keg and faucet. Length and inside diameter are important.
 

beergorila

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Yeah I also did something similar with shaking the keg at 30 psi for a few minutes, but without waiting any time for the keg to rest on high pressure. However, now several hours later having let the keg sit quietly in the fridge off gas, I am getting 95% foam 5% liquid, and the beer itself tastes FLAT.

I have 6' of 3/16" line and am dispensing at 12 psi. There is considerable foam in the beer line -- would that convert the beer coming out of the keg into foam if I can't clear it out, or is something else going on?

How in the heck could it be overcarbed, yet taste entirely flat??
 
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