Pouring Beer on Nitro
Q: I am having an issue with a stout in which I used 75% nitrogen/25% carbon dioxide beer gas mix. It’s been kegged for six weeks at 33 PSI and held between 36–37 °F (2–3 °C). The beer barely cascades (basically nothing) pouring from a stout faucet. I’m new to using nitro, but have been brewing for 15 years and have no issues with my other beers. I’m starting to question if the stout tap is good.
— Ken Schretlen • via email
A: When it comes to pouring stout, there is a clear gold standard to match: That’s Guinness. A brief review of a few key things known about Guinness draft stout helps troubleshooting. According to numerous references, Guinness contains a paltry 1.2 volumes or 2.4 g/L of carbon dioxide and about 55 ppm of nitrogen (level reported from a brewing scientist in England with knowledge about this specification). These gas specifications align with beer equilibrated with a 75% nitrogen/25% carbon dioxide gas blend at 33 PSI and 36 °F (2 °C).
Although U.S. nitro brewers use the gas mix and conditions you used, Guinness specifies in their Draught Quality Standards publication a 70% nitrogen/30% carbon dioxide gas blend at 32–40 PSI for kegs stored at 46–50 °F (8–10 °C) and chilled in-line to the faucet to 39-43 °F (4–6 °C). This reflects differences in beer handling practices in the different parts of the world selling Guinness.
If low nitrogen content is your problem, one cause is insufficient headspace in your keg. An easy thing to try is to simply pour off some beer, let your beer rest to re-equilibrate or lay your keg on its side and do some shaking to speed things along, and check to see if you have more cascading. If you do, it’s an indicator that this strategy is working. Either keep rocking your keg until you hear gas flow stopping or let your beer sit for several days to allow gas transfer between the headspace and beer to occur.
Another possible cause of no cascading is insufficient velocity flowing through the faucet. The classic Guinness faucet requires turbulent flow occurring as beer is forced through the five tiny holes in the restriction plate or so-called jet disk. Some brewers make the mistake of reducing the keg pressure to “normal” beer pressure before serving or make the mistake of trying to balance the draft system by using the line diameter and length rules used for normal carbonated beer. Both mistakes result in low velocity and little to no gas breakout as beer flows through the jet disk. Guinness provides a 12 second target for the first part of their classic two-part pour. This translates to 1.25 ounces (37 mL) per second. If your flow rate is too slow and your keg pressure is about 33 PSI using a 75/25 gas blend, you have too much line restriction or your restriction plate is clogged. Start by checking the restriction plate; if clear, it’s time to do some line replacing using a minimal line length between keg and faucet.
In my experience, poor cascading and foam formation in nitro beers is typically caused by inadequate dissolved nitrogen. Although high gas pressures can be used to increase the gas transfer rate using what I call the crank and shake method, gas control is approximate at best. The most reliable way to quickly nitrogenate your beer is to lay the keg on its side, position your gas cylinder above the keg to prevent beer from flowing into your gas line, pressurize the gas line, connect it to the keg with the gas line positioned at 12 o’clock to prevent excessive foaming, and allow the headspace to pressurize.
Once the keg is pressurized to ~33 PSI, begin rolling the keg back and forth. As gas dissolves into the beer, pressure in the line drops, and the regulator allows gas to flow. This is audible and is a direct indicator of gas flow into the beer. As dissolved gas content approaches the equilibrium condition and gas flow slows, you should hear a change to the sound of the operation. When you can no longer hear gas flowing, you are close to being done. I find it works well to allow the keg to settle for about 15 minutes and repeat the rocking step. When no gas flow can be heard when rocking your rested keg, it’s time to let the keg rest upright for an hour or so before pouring a pint. If you don’t like this idea, simply connect your keg to your gas cylinder, set the regulator pressure to ~33 PSI and let the system sit for a week.
