Brewing Links:
Kegging Homebrew
Yes. It's as cool as it sounds and worth every penny.
One of the questions I see a lot is "How many kegs can you
carbonate and dispense with a single fill on a xx pound CO2
tank"? There are a lot of variables of course based on how many
volumes you carb each keg to (volumes) and how much you waste into
the atmosphere. The typical average in my opinion is 2 volumes
meaning there will be 2 times as much gaseous CO2 dissolved as there
is beer. Example, 5 gallons of beer take on 10 gallons of CO2. It
will take another 5 gallons of CO2 to push all that beer out of the
keg. The real issue is figuring out how much liquid CO2 it takes to
create a certain number of gallons of gaseous CO2.
According to
http://www.ca.airliquide.com/en/business/products/carbon_diox/index.asp
, 1 pound of CO2 (it's sold by the pound) is equal to 8.741 cubic
feat of gaseous CO2 at sea level / 70F. If my logic serves me, this
volume would actually be halved at typical carbonation pressure of
say 14 psi (2ATM) for 4.37 cuft. I'm going to ignore the
temperature.
5 gallons is .668 cubic feet. 4.37cuft (1lb co2) divided by
.668 = 6.54. That means 1 pound of liquid CO2 is 6.54 volumes in a 5
gallon keg. For example, that would be enough to carb two kegs to
2.25 volumes and dispense both to empty. So if 2.25 volumes was an
average carb level, and there was no wasted Co2 on purging/venting:
| CO2 Tank Size |
Total Volumes 5 gal @ 14psi |
Total Kegs, Carb 2.5 vol + Dispense |
| 2.5 lb |
16.35 |
5.3 |
| 5 lb |
32.7 |
10.6 |
| 10 lb |
65.4 |
21.2 |
| 20 lb |
130.8 |
42.4 |
I admit, I don't understand the ideal gas law in the slightest so I
can't really know how the temperature of the beer is playing on the
volume requirements. However, Micromatic, an authority on keg
dispensing claims that it takes about 1lb of CO2 to "DISPENSE" a 1/2
barrel. This would mean that it takes 1/3rd or .33 pounds per volume
on 5 gallons. Remembering that carbing to 2 volumes and dispensing
actually takes 3 volumes, that's 1 pound per 5 gallon keg. On the
same page, the chart shows a 20lb tank capable of dispensing at
least 62 five gallon kegs but you have to remember that dispensing
only takes ONE volume so carbing will require 200% more gas. So, the
number I'm comfortable with right now is "about 1 pound per 5 gallon
keg".
So how much pressure should you apply to the kegs?
It depends on the temperature of the beer inside and how much
carbonation you want. Here's a chart:
http://www.northernbrewer.com/instructions/co2.htm
I use 10-12psi for most of my beers at 40F.
Methods of carbonating kegs using CO2 under pressure:
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://sdcollins.home.mindspring.com...rbonation.html 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.
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.
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?
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