A while back, reader Joe J. asked
Can you school us on how you nitrogenate your beer? I am upgrading soon, and would love to have some insight.
… to which I reluctantly agreed, because there are few things I dislike more than Imperial pints of dry stout poured on mixed gas. So with my usual battery of caveats (“this is just how I do it and it works for me, but it’s not the only way, YMMV” etc.) let’s dig in.
First, some brief theory: nitrogen dispense – AKA mixed-gas dispense, nitro pour, probably some other terms I can’t recall at the moment – is pouring kegged beer with a blend of nitrogen and CO2 (instead of just CO2). It was designed and implemented commercially in Ireland and the UK to mimic the effects of hand-pumped dispense without the loss of shelf life that accompanies air influx into the spiled cask.
The gas blend is usually in the neighborhood of 70% N to 30% CO2, an approximation of atmospheric air. Because nitrogen is less soluble in liquid than CO2, it gets knocked out of solution easily and the beer gets quite degassed as it pours, which creates that iconic cascade of bubbles and a creamy, smooth mouthfeel in a beer with a pretty low delivered carbonation level.
Assuming you already have a homebrew soda keg system, here’s the list of additional necessaries:
- Nitrogen tank filled with beer gas. Nitrogen tanks are pressurized to a much higher level than CO2 cylinders, and they have a threaded female port for the regulator. “Beer gas mix” is what our 70/30 N:CO2 blend is usually known as when you go to fill it up.
- Regulator for nitro tank (plus gas tubing & QD for your keg). Nitrogen regulators are rated for higher pressure than CO2 regulators, and have a male threaded fitting for the female port on the nitro tank. Fittings for gas tubing should be the same as for your CO2 system.
- Stout faucet (plus bev tubing & QD for your keg). It is physically possible to dispense nitrogenated, kegged beer through a regular old beer faucet, or even a plastic cobra tap, but in my experience it’s a bit like starting the engine but not driving the car all the way home. Without the restrictor plate of a stout faucet, I have found the cascade of bubbles is largely lost, the texture isn’t quite the same, and the head on the pint is less impressive. These faucets have a two-way valve that allows regular pouring when the handle is pulled forward, and then a “foaming” position when it’s pushed back to top off the last 1/3 or so of the glass, creating a very densely-knit cap of foam.
- Diffusion stone inside the keg. Because nitrogen is less soluble than CO2, pushing the beer gas through a diffusion stone (0.5 microns or so) inside the bottom of the keg ensures that the bright beer will get adequately saturated. It’s possible to Macguyver a stone clamped onto a couple feet of tubing with the other end snugged over the gas-in tube inside the keg, but a rig like this (storebought or homemade) is a bit more elegant.
- Chill & fine the beer prior to kegging. This is key, because yeast floccs, trub, and other solids will clog up the restrictor plate in the stout faucet.
- Rack clear beer into keg & insert diffusion stone.
- Connect to beer gas blend & apply pressure. I usually start at about 35 psi and adjust as needed. Normal dispensing pressure for me is usually 25-35 psi, and I prefer to err on the high side.
- Wait, then pour. Give it a day or so, depending on how cold the beer is. If I’m in a hurry to get it online and have a stout stat, I have been known to turn the pressure up to 45 psi or so and dispense immediately (what I did for the pint photos shown in this post), and gradually adjust the pressure downward over time as the beer absorbs more gas.
Hope this helps, Joe! Now I need to find a way to properly dispose of this nitro-poured stout.