When it comes to draft beer gas, there is a lot of confusion among both commercial and residential draft beer system owners. This results in poor practices and general misunderstandings about how the pressure (gas) system works and how to apply the right gas at the right pressure to achieve perfect draft pours every time.
Hopefully, we can point out the basics of the draft beer gas system and avert any further confusion.
To properly operate your draft beer system it is important to understand the nature of the pressure side of draft beer systems.
First let's take a look at what's available in gases:
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– N2, CO2, O2, Pollution, Pollen, Bacteria and Wild Yeast - air is bad for beer as it causes oxidation, which in turn ruins the flavor of beer. Air makes beer taste like wet cardboard. Even though air contains some parts of the good gases for beer (Carbon dioxide and Nitrogen), the presence of oxygen makes it unusable in a draft beer pressure system. That doesn’t mean that it is not used. Some bars still use compressed air to pressurize their draft systems. Air is also used to pressurize kegs via a hand pump at parties. In an application like this the air is acceptable because the beer will be finished within a day.
– CO2 or Carbonic Acid. This is a naturally occurring gas that is highly soluble (dissolves easily) in beer. In fact, CO2 is a natural component of beer as a major byproduct of the fermentation process, another being alcohol. CO2 gives beer its characteristic head and provides a slight bittering in taste (a desirable quality in beer). CO2 also provides effervescence that helps “lift” the beer’s aromas into the drinker’s nose and palate.
– N2. Another naturally occurring gas that is insoluble (hard to dissolve) in beer. Nitrogen has two similar purposes for use with draft beer: (1) to allow high pressure dispensing through heavily restrictive apparatus (causing notable frothing) as in Guinness and similar products; (2) to allow high enough gas pressures to overcome the resistance inherent in long beer lines. In both of these cases the goal is to push the beer at high pressure but not alter the carbonation of the beer as it sits in a keg. This is accomplished by using insoluble Nitrogen mixed with the soluble CO2. More on gas mixing in a moment.
– (Ar) Often used by brewers to protect wort (unfermented beer) and beer from oxidation. It is also widely used in winemaking. This is an inert gas that is relatively insoluble (compared to CO2). However, it is expensive and not practical to use in draft beer systems. I only mention it here because it appears as a preservative in some wine systems and may work its way into beer service in the future, but most likely not for pressure purposes.
– This pre-blended gas is a blend of Carbon Dioxide (25%) and Nitrogen (75%) made specifically for use with Guinness Stout and other similar beers. This mix is used to allow the high pressures needed to force the beer through a restrictor plate in a specialty faucet. This is to create the frothy pours characteristic of this style. In this type of application, the use of CO2 alone would quickly over carbonate the beer and pouring would be impossible. This mix is also very commonly, but incorrectly, used to pressurize the long line draft systems common in many restaurants and bars. This is not the proper ratio of mixed gases to serve standard ales and lagers. Beer Gas is however, the only pre-blended gas commonly available – creating confusion over its proper usage.
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