May 26, 2013 at 8:08 pm #388
I’m about to try something, hoping someone’s already done it and can save me the trouble. In a nutshell, I’m taking a normal abv, normal TG ale and carbonating it via top pressure.
Keg, with beer, at X temp, knownish CO2 in solution, into a keg, math out the temp and volume differentials and hit the keg with proper pressure, wait and see if it hits the proper carb level w/o active tank pressure. I have a gauge I plan to rig onto the gas QD to see when it bottoms out.
This probably sounds worthwhile only to those who nor ally keep their tank off to a kid acci leakage.
Any thoughts are welcome, including those on the errors of the Henry coefficient on various alc content. If I can even get close I think it would be cool. “Set it and forget it” carbonation.May 29, 2013 at 10:18 am #389
Let me see if I understand what you are trying to do…
You want to take your beer as normal and sort of supercharge it with a blast of CO2 at say like 50psi, hoping that it will absorb and end up at the correct head pressure an temperature for a given # of vols?May 29, 2013 at 11:54 am #390
OK so I’m going to assume that I was right and keep this rambling going…
Using the ideal gas law Pv-nRT you can calculate the following situation:
You want 2.3 vols of CO2 in finished beer
Beer finishes fermentation with about .9 vols in it already (assume 65F ferm temp)
your kegerator is holding at 40F
You live in Fort Collins and the elevation is 5000ft
You have .1 gals of headspace in the keg – not really sure what is realistic (need to measure)
You would need to charge the keg with 83.4 PSIG of CO2 to get the stated vols…
However I have no idea how long this would take to absorb, and I would expect the rate of dissolution to decay exponentially. This would mean that the final absorbtion could take weeks or months, I don’t really know – you could possibly overcome this by charging a couple extra PSI…
The timing could be calculated if you measured the dissolution coefficient. That could be tricky in and of itself though.
Conclusion – yes it can be done but might take forever. Some experimentation needed.
DaveJune 1, 2013 at 8:40 am #398
Yep, exactly what I was talking about, Dave. And your made-up numbers aren’t far from mine. (There’s probably more like a quart of headspace.) I’m sure you’re right about the absorption curve. The real point of this would to allow for “setting and forgetting” as the beer continues to clear in situ. I plan on trying it when I get off my butt and keg some of this stuff next week. If I can even get 90% or so in a couple of weeks that would be functional.June 1, 2013 at 8:43 am #399
But how do you measure the difference in co2 in the headspace against the final dissolved co2 for a gross need in the headspace at the start? For what I’m doing, I can just go a little heavy, see how long it takes to get where I want and bleed it.June 4, 2013 at 12:06 am #404
So here we go. This ball-lock keg weighs 8 pounds 8.6 ounces, nearest I can tell. Totally full spilling out the top, it weighs 52 pounds. Not accounting for altitude and pretending the water is distilled, that works out to 5.21 g.
My beer is SG 1.011, and there’s 48.8# minus the tare, so about 4.78 g. Sitting at 64 F it looks like max CO2 is .82 vols, but I bet it’s less since it fermented at ~66. Let’s call it .8 vols.
478/521= 92% full.
According to BeerSmith, to get 2.6 vols I need 4.25# “added” at 38F. That’s only ~54#.
What am I doing wrong?June 4, 2013 at 11:32 am #405
SO I’m not quite sure how you are converting vols to #’s and I don’t think it’s right. There should only be about 12 grams of CO2 in the keg after being fully carbonated, not very easy to measure on top of 50lb of beer.
They way I’m doing it, and would be happy to share my spreadsheet after cleaning it up, is basically this:
[mols CO2 in the final headspace] + [mols CO2 in the final beer (@2.6 vols)] – [mols CO2 already in the beer after fermentation] = total mols of CO2 needed to get to 2.6vols (accounting for headspace) @ 40F @known volume of beer
Take this number and convert from mols back to pressure at the known headspace. This will give you a pressure to set the headspace at (assuming temperature is the same)
Theoretically if all the CO2 absorbed down to equilibrium, then your headspace will end up at the pressure that you would normally set your regulator to with the “set and forget method”
So if I plug your conditions into my spreadsheet, I come up with 48.5 psig (gauge) put into the headspace should get you to 2.6 volumes at 40F.
The big unknown is how long will this take to absorb. I haven’t been able to find any good information on CO2 dissolution into beer. I think it will be affected by pressure differential, temperature, final gravity, and alcohol %. If you find any information on this, please pass it along.
I am curious to charge the headspace, put the keg on it’s side, then shake the hell out of it and see what it goes down to…
DaveJune 17, 2013 at 2:19 pm #442
To figure this out, we need to run an experiment where we measure the rate the CO2 dissolves into the beer. Do you have a beer available to do this? If not I think I’ll have one sometime next week.
First we need to measure an empty keg charged to high pressure, and make sure it doesn’t leak. This is the baseline, should be some fluctuation but hopefully the avg is steady.
Then fill the keg with beer, charge the headspace and measure/record the pressure of the keg every 1-2 hours throughout a few days during the daytime. This should give us an idea of how long it would take.
I think this could be really cool, the amounts of CO2 that I get from doing the math are really close to what is kept in those small CO2 cartridges you sell at H&B (~12g). You may just be able to dump the whole cartridge into the headspace and just wait a few days to get close.
I am also wondering if you could just break off a measured piece of dry ice, toss it in, and let it go. As long as you don’t add too much it shouldn’t blow up (famous last words)June 17, 2013 at 2:28 pm #443
Yeah the headspace volume was just figure how much more co2 is needed beyond the beer carbonating. If the keg holds a gross 5 g and its half full you’ll need more co2 than if its 9/10 full, right?
Anyway, your 48.5 is not far from my 54#. Sounds like we have a ballpark.
I’m kegging today. I think I have the parts to rig a gauge on the out post.June 17, 2013 at 2:36 pm #444
…except I’m out of gas. Tomorrow.June 17, 2013 at 2:38 pm #445
Yes you are right, but with the larger headspace you can fit more gas at lower pressure, so if you had say a 3 gallon headspace you would only need to charge it to about 19psig.
I’m still worried that I’m missing something key, so this should be a fun experiment!June 17, 2013 at 3:02 pm #446
Packrat strikes again!
I was thinking I’d have to rig a minireg up to a QD, but digging through my pile I found this from years ago. Shit like this makes it amazingly difficult to ever throw anything away.
19/32 thread (gas post thread) to a 0-100psi gauge w/shraeder valve.
Just need to check the gauge and make sure there’s no leaks, get a chuck on the gas line and set it.
Reminds me of the time I threw out the call for a scanner to borrow, and then “neverminded” after I found TWO in my garage. Two.
June 17, 2013 at 3:04 pm #448
- This reply was modified 4 years, 8 months ago by Taylor Caron.
Awesome! I’m also a packrat, every time I start throwing things away I regret it a few weeks later. Every. time.June 17, 2013 at 9:24 pm #450
Have been priming in the keg, but recently I have resorted to doing this sort of thing more commonly because I have no way to get the gas hose into my fridge. Never run through the calculations. Just eyeball it. I push 20# (will go look at the gauge to verify) or so onto the beer maybe a half dozen times or so before putting in the fridge (at whatever the garage temp happens to be). Only takes a few days to absorb. Just use head pressure to fill a couple glasses and top up the gas every few pints when the fridge door is open.
So now that you have whipped out an equation, guess I’m gonna have to try to work it out. If we have some idea of the variance for each of your parameters, we can estimate a mean for the amount of C02 required with some error.June 17, 2013 at 9:30 pm #451
Really curious what this means “nor ally keep their tank off to a kid acci leakage”. Speaking in tongues?
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