Nitro Beer

The process of adding nitrogen to beer is referred to as nitrogenation. This is somewhat of a misnomer since nitrogenated beers also contain carbon dioxide and the gas blend used for the process is usually 75 percent nitrogen and 25 percent carbon dioxide. This mix is used to dispense draught Guinness Stout and is easy to find in markets that have draught Guinness.

Nitrogenated beers typically contain very low amounts of carbon dioxide, around 2.4 g/L or 1.2 volumes, and an even lower concentration of nitrogen of about 20 mg/L. “Typical” beers contain about 5 g/L of carbon dioxide and no nitrogen. The concentration of nitrogen is much lower than the carbon dioxide content because nitrogen is not very soluble in liquids. When dispensed through a special faucet, the nitrogen “breaks out” of the beer and forms very small, stable bubbles. Nitrogen foams are much more stable than carbon dioxide foams because the atmosphere is about 79 percent nitrogen and there is not much driving force between the gas concentration in the bubble and the concentration in the atmosphere. That’s why “nitro” beers have such awesome, stable foam. The density and creaminess of the foam also adds a terrific mouthfeel to the beer.

Like many brewers, Mr. Wizard loves nitrogenated beers and has some rules of thumb on the procedure. For starters, don’t bother nitrogenating any beer unless you have the proper faucet. There are many “stout” faucets on the market that are based on the Guinness faucet. All of these faucets have a disc with small holes inserted in the beer flow path and a device called a “flow straightener” placed after the disc. As beer flows through the holes in the disc there is a large reduction in pressure and this pressure drop causes the nitrogen and carbon dioxide to break out of solution. If the gas blend is just right you get a great glass of milky looking beer that settles out with a perfect head.

The other piece of equipment that is very important is a carbonation stone. I recommend the type of stone that can be connected to a stainless-steel rod and attached to the “out” fitting on a Cornelius soda keg. The stone is important because nitrogen is insoluble and it really helps to have small bubbles dispersed in the beer during the nitrogenation procedure. The key is getting the right gas blend. Too much carbon dioxide results in a large foamy head that doesn’t settle properly — and too much nitrogen results
in “wild beer” that will foam uncontrollably. Too little dissolved gas produces a pint that just seems flat. Now for the steps required for proper nitrogenation:

Step 1: Rack your beer to a keg after fermentation is complete (add finings if desired) and pressurize the headspace of the keg with mixed gas (75 percent nitrogen and 25 percent carbon dioxide) to a pressure of 10 to 15 PSI. This pressure is used to seal the keg and does not serve to nitrogenate the beer. Do not pressurize with 100 percent carbon dioxide because the beer will absorb too much.

Step 2: Transfer the keg to the coldest place you can find, preferably a refrigerator set at about 34 °F (1.1 °C), and allow the beer to clarify. I recommend about two weeks.

Step 2 (alternate): Filter the beer after holding cold for about one week. I have found that nitro beers pour much better when they are free of yeast.

Step 3: Make sure your beer is cold (between 34 and 38 °F/1.1–3.3 °C)) and connect the mixed gas supply to the carbonating stone and set the pressure regulator to 30 PSI. Gas will bubble though the beer until the headspace pressure reaches 30 PSI. After the headspace pressure is at 30 PSI, slowly loosen the pressure- relief fitting on the top of the keg until you hear a very low flow of gas escaping from the fitting. Allow the mixed gas to slowly bubble through the beer for 30 minutes. (If foam begins to come out of the fitting, tighten the fitting and allow the beer to rest for 30 minutes before continuing the slow bleed.) After this 30-minute purge, tighten the pressure-relief fitting and allow the beer to rest for 30 minutes, then do another 30-minute purge.

Step 4: Hook up the mixed gas to the headspace of the keg and set the pressure regulator to 30 PSI. Let the beer sit still for a few hours before pouring.

Step 5: Pour yourself a pint of nitro homebrew! If the foam seems excessive you should use a lower pressure the next time around and if it seems a bit flat you can repeat Step 3, using a higher pressure.

Response by Ashton Lewis.