CO2: The Gas Source For Dispensing Keg Beer

CO2 dispensing keg beer

Gas goes into the keg and beer comes out simple, right? Take a few minutes and understand that the first component on the pressure side of a draft beer system – the gas source. You need to move the beer from the keg to the faucet, this is called applied pressure. The gas selected should only be viewed as the pressure source of the system and should never change the carbonation level of the beer as prescribed by the brewery.

CO2 is the best gas source for dispensing draft beer as CO2 is naturally generated during fermentation. It is equally important to note that compressed air is never recommended as a gas source. The brewing industry invests millions of dollars in keeping air (oxygen) out of the keg package and, therefore, applying air pressure to the beer keg is detrimental to beer quality. Air compressors are rarely cleaned and the oil from the compressor quite often mixes with the air and the result will be an off smell and taste to the beer.

In any draft beer system, the CO2 gas cylinder and pressure regulator are crucial components that start the process of dispensing beer. The filled CO2 tank provides gas that is monitored by a regulator and controls the flow of beer. Generally used in direct draw systems for low-volume dispensing. CO2 cylinders are available in different weights, i.e., 2 1⁄2, 5, 10, 15, 20 and 50 lbs. CO2 cylinders are selected based on the weekly keg volume. For example, a 5 lb cylinder may be used in a single keg kegerator where draft beer is sold in limited volume, a 20 lb cylinder is needed where there are 4 or more kegs on tap in a kegerator.

A full gas cylinder has approximately 800 PSI, far too high for dispensing purposes, this is where the regulator comes in. The regulator controls (regulates) the amount of pressure (PSI) used to dispense the beer, so you get a consistently perfect pour.

CO2 displaces beer at a continuous pressure, replacing the poured beer by occupying the space that otherwise would be empty in the keg. Empty space is referred to as “head space.” CO2 fills the head space and maintains the pressure inside the keg. That pressure is set via a pressure gauge that uses pounds per square inch (PSI) to release the right amount of gas into the keg. Maintaining a constant PSI keeps the beer perfectly carbonated by preventing the CO2 that’s dissolved in the beer from leaking out of the keg.

NYSRA February 2019 728×90


It’s always best to check with your beer wholesaler’s draft technician as to setting the regulator pressure. For a keg refrigerator at 38˚ F, the recommend CO2 pressure is between 12–14 lbs for most domestic beers. This pressure will maintain the level of carbonation that the breweries specify. If the beer is dispensed with too low of a pressure, over time the CO2 that is dissolved in the beer will break out. This will result in flat beer. If the beer is dispensed with too high of a pressure, over time more CO2 will be absorbed into the beer and the result will be foamy beer.


As a general rule of thumb, it takes about a 1⁄4 lb of CO2 to dispense a 1⁄4 barrel of beer and a 1⁄2 lb of CO2 to dispense a 1⁄2 barrel of beer. A 5 lb CO2 cylinder will dispense 18 – 20 1⁄4 barrels or 9-10 1⁄2 barrels.

Tips for Maintaining Pressure

  • Store your gas cylinder upright
  • Identify the proper PSI, lagers dispense at 10-12 PSI

Signs of Too Much Pressure:

  • Fast pour
  • Foamy beer
  • Over carbonation

Signs of Not Enough Pressure:

  • Foamy beer
  • Large “soapy” bubbles
  • Bubbles rising to the beer line

Troubleshooting, Beer Not Pouring:

No gas? Check:

  • Regulator shutoff is in-line with gas hose, if it is at a 90 degree angle the gas is turned off
  • High side pressure gauge at zero, there is no gas in the cylinder

Gas Leak? Check:

  • Use a light mix of liquid soap and water to check all the connections: fittings, clamps, shutoffs and the regulator for escaping gas