I have an existing keg of beer that I would like to switch to beer gas. Is this feasible? Are there any problems with doing this?
- If you plan to serve the beer through a stout or creamer faucet then it's a good idea to reduce the carbonation in the beer to about 30% of what it was. This can be done by also bleeding off most of the CO2 in the headspace, possibly several times. For example, if the keg is currently 1/3 full of beer, then bleeding the headspace and leaving will reduce the overall carbonation in the beer to 1/3. If the keg is 2/3 full, then you'll need to bleed it 2-3 times, waiting a couple of days for the pressure to increase each time. You could skip this, but you'll end up with a lot of foam in the glass.
Adding beer gas already mixed in the cylinder:
- bleed the gas from the keg until it's almost empty then fill the headspace to the desired pressure with the beer gas.
Adding pure nitrogen, rather than ready mixed:
- Reduce the pressure in the headspace. Bleed the headspace until the pressure is about a quarter of your ideal serving pressure. Beer gas is often served at 30 psi with a stout faucet, so 7 psi for the CO2 pressure.
- pressurize to your target pressure (say, 30psi) with nitrogen.
- The keg is now full with a mix of 25% carbon dioxide and 75% nitrogen.