Know your gas: Understanding the difference between Co2, Nitrogen and blended systems
What is ‘gas’? According the Brewers Assocation, gas is “a group of molecules flying around at high speed. When contained within walls, they create pressure. When one wall is liquid, they constantly enter and exit.”
We see ‘gas’ exiting our beer everytime it is poured from the tap. ‘Foam’ and ‘bubbles’ are essentially gas leaving beer; as gas leaves beer, it allows hop, malt, spice aromas to escape the liquid. This is why some glasses are curved at the top, in attempt to trap some of these aromas and let them linger.
I am often asked questions about the type of ‘gas’ we use in our store, to which I respond, “Well, our draught system uses a blend of 70% Co2 and 30% Nitrogen. ” I never go quite beyond that, and to be honest I’m not sure there is a real reason to, but…for the sake of blogging, let’s explore gas!
Carbon dioxide is a byproduct of fermentation. It is incredibly soluble in liquid, most beers having a dissolved Co2 volume of 2.5..ish. Co2 levels depend on temperature, and pressure conditions between gas and beer. The end goal is equilibrium; the co2 volume in beer should remain constant, given the correct temperature (a raise in temperature results in co2 that is LESS soluble) and pressure (amount of co2 pushing onto the “wall” of liquid inside the keg.
See the chart below for specificity according to style.
|British Style Ales||1.5 – 2.0 volumes|
|Belgian Ales||1.9 – 2.4 volumes|
|American Ales and Lager||2.2 – 2.7 volumes|
|Fruit Lambic||3.0 – 4.5 volumes|
|Porter, Stout||1.7 – 2.3 volumes|
|European Lagers||2.2 – 2.7 volumes|
|Lambic||2.4 – 2.8 volumes|
|German Wheat Beer||3.3 – 4.5 volume|
Co2 is measure by PSI, or pounds per square inch. Long draw systems (draught systems that require long distance tubing from keg to tap, require close to 22psi to maintain this Co2 equilibrium. Short draw systems require closer to 12psi.
Also note that as elevation rises, atmospheric pressure drops. So, if you are in Denver, you will need more pressure to push the beer out than if you were at sea level. Make sense?
Nitrogen is used in long draw draught sytems to push the beer through longer lines. The reason Nitrogen is used has to do with the fact that it is odorless,tasteless, and significantly less soluble in liquid than CO2. If a long draw system were to push 100% Co2 through the line, the beer would be OVER CARBONATED, resulting in foamy beer. Both of our draught systems at Growlers To Go use a long draw system with 70/30 blended gas, to prevent over carbonated, foamy beer, thus maintaining a state of equilibrium with soluble Co2 volume in keg, and pressure of gas pushing the beer out! Other gas blends of 60/40 and 80/20 have been tested, but results show that 70/30 is the best ratio to maintain perfectly carbonated beer.
Resources for further reading on gas and gas blending
For homebrewers- http://learn.kegerator.com/force-carbonating-beer/