Monthly Archives: May 2016

Brewing Log

Beer gas, partial pressure, psia, and psig,oh my!

The question of what pressure to run your beer gas setup seems to be a topic folks struggle with.  Below is my attempt to clear this up.

I have easy accessibility to a 25/75 blend of CO2 and N2.  When you see a blend the first number will always be CO2 the second N2.

I will use a target of 1.2 volumes of CO2 for the bourbon barrel stout. This is the same level used for Guinness.

Using a calculator like brewersfriend and my kegerator temperature of 38° we are informed we need a pressure of -2.5 psi to get 1.2 volumes. The important thing to note here is the result we are given is in psig for gauge.  Our gauges are set to read 0 at 1 atmosphere or 14.7 psi at sea level.

  • The first step is to first convert to psia or actual by adding the 14.7 psi for 1 atmosphere of pressure. If you are at high elevation you should look up the appropriate value for you.
    -2.5psig + 14.7 = 12.2 psia
  • Next we account for the fact that our gas is only 25% CO2.
    12.2psia / 0.25 =  48.8 psia
  • Now we convert back to psig so we know what to set our regulator to.
    48.8 psia – 14.7 = 34.1 psig

McDantim has some great calculators. I use this one.  It accounts for some additional factors like ABV and elevation.

It is recommended to force carb your keg a little on CO2 just to get to your wanted volumes then place the keg on the beer gas.  If you are running the right pressure it will stay perfectly carbonated.
The N2 tank fits on the hump with the CO2 tank and a 5 gallon ball lock keg.  On the floor is three more ball lock kegs and a commercial 1/6th keg from a local brewery.
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Brewing Log, Keezer

Beer Update, Kegerator Upgrade

Several updates today.  The whirlpool IPA is ontap and I am very happy with the result.  It has that juicy hop character while not being very bitter.

I also picked up my share of the bourbon barrel stout and it is awesome.  Far better than I was even expecting.  It has a nice nose on it but the flavor is not overpowering and complements the beer very well.  Now I need to determine what I am going to do with it.  I think I will bottle one keg and serve the other on nitro.

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That brings me to my nitro upgrade. In a prior post I discussed a faux nitro setup using CO2.  This works but I found it was very easy to forget to bleed the pressure back down to the correct level each night.  This resulted in over carbonation several times. Rather they attempt to fix the user… I purchased a 20 cu-ft nitro tank and regulator. It seems there is a lot of confusion around what pressure to run beer gas at so I will write a follow up post discussing that.