Grinder12000
Well-Known Member
I'm not talking a "problem" but instead of 2.0 maybe the beer is at 2.4 or something (I have no clue really).
But in theory will a small purge help?
But in theory will a small purge help?
Will a quick purge help a small over carb?
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Short answer: NO
Long answer: 1 gal of beer carbed to 2.4 volumes contains the equivalent of 2.4 gal of CO2 at atmospheric pressure. So, if you had 4 gal of 2.4 vol beer in your keg, the beer would contain 4 * 2.4 = 9.6 gal of CO2. To reduce the carb level to 2.0 volumes, you need to get 9.6 - 8.0 = 1.6 gal of CO2 out of the beer. Since you have about 1 gal of headspace, each venting would release 1 gal of CO2 at whatever the current keg pressure is. For 2.4 volumes at 40°, the keg pressure would be 11 lb. 1 gal of CO2 @ 11 psi = 11 psi / 14.7 psi [atmospheric pressure] = 0.75 gal @ atmospheric pressure. Thus two ventings would release about 1.5 gal of CO2, IF the beer carb level was allowed to equilibrate between ventings.
Reaching equilibrium (or close to it) would take several days. If you didn't wait for equilibrium to be reached between ventings, then getting your desired carb reduction would take more ventings. If your keg was fuller, the headspace would be lower, and each venting would release less CO2, so you would need more ventings.
Calculating how many purges and how long between purges is complicated (i.e. I haven't figured out how to do it yet), so just venting every hour or so until you get the carb level where you want it is the easiest way to go.
If you want to decarb in a hurry, check out this thread: https://www.homebrewtalk.com/showthread.php?t=127655
Brew on
Long answer: 1 gal of beer carbed to 2.4 volumes contains the equivalent of 2.4 gal of CO2 at atmospheric pressure. So, if you had 4 gal of 2.4 vol beer in your keg, the beer would contain 4 * 2.4 = 9.6 gal of CO2. To reduce the carb level to 2.0 volumes, you need to get 9.6 - 8.0 = 1.6 gal of CO2 out of the beer. Since you have about 1 gal of headspace, each venting would release 1 gal of CO2 at whatever the current keg pressure is. For 2.4 volumes at 40°, the keg pressure would be 11 lb. 1 gal of CO2 @ 11 psi = 11 psi / 14.7 psi [atmospheric pressure] = 0.75 gal @ atmospheric pressure. Thus two ventings would release about 1.5 gal of CO2, IF the beer carb level was allowed to equilibrate between ventings.
Reaching equilibrium (or close to it) would take several days. If you didn't wait for equilibrium to be reached between ventings, then getting your desired carb reduction would take more ventings. If your keg was fuller, the headspace would be lower, and each venting would release less CO2, so you would need more ventings.
Calculating how many purges and how long between purges is complicated (i.e. I haven't figured out how to do it yet), so just venting every hour or so until you get the carb level where you want it is the easiest way to go.
If you want to decarb in a hurry, check out this thread: https://www.homebrewtalk.com/showthread.php?t=127655
Brew on
OP
OP
Grinder12000
Well-Known Member
Yea - I saw that. It's not like I have foam or anything - just wondering how to adjust with ease if needed. I see I need a regulator that has two separate adjustable pressure gauges . . or something.
I also see I LOVE kegging over bottling and will welcome alcoholism! 143 batches of bottling and I finally saw the light (and had the money).
I also see I LOVE kegging over bottling and will welcome alcoholism! 143 batches of bottling and I finally saw the light (and had the money).
if you have a spundling valve you just put it on the keg and it sorts itself out over a day or so. basically, its a pressure-relief valve that can be made for about 30 bucks in parts, people use them to naturally carb beer in kegs/fermenters.
set it to the psi you want, snap it onto the post and it'll start bleeding air until it hits whatever psi level you've set it at.
set it to the psi you want, snap it onto the post and it'll start bleeding air until it hits whatever psi level you've set it at.
A spunding valve is a great "set and forget" method to let the carbonation come to equilibrium at a different value. The downside to a spunding valve is that it's the slowest way to lower the carb on a beer. The reason for this is that with a spunding valve the average difference between the equilibrium CO2 pressure for the current carb level and the valve pressure setting is smaller than the average pressure difference when purging. The rate of CO2 loss will be roughly proportional to the equilibrium CO2 pressure for the current carb level and the headspace pressure. The larger the pressure difference, the faster CO2 will come out of solution.
Building a spunding valve requires the following items:
- Gas QD for type of keg you have
- Pressure gauge https://www.amazon.com/gp/product/B003B87LNW/?tag=skimlinks_replacement-20
- Adjustable pressure relief valve https://www.amazon.com/gp/product/B007GDY3CU/?tag=skimlinks_replacement-20
- Tee fitting https://www.amazon.com/gp/product/B000BQUTBS/?tag=skimlinks_replacement-20
- 1/4" hose nipple https://www.amazon.com/gp/product/B002SAO7XQ/?tag=skimlinks_replacement-20
- Short length of gas tubing
- Hose clamps
Brew on
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