As with the thousands of pub landlords in the UK, beer gas thrives under pressure. That pressure is used to maintain quality while providing movement for the beer.
For me personally the research into the role and purpose of gasses in the pubs and cellar systems around the country has highlighted the engineering and brewing elegance of the process and its evolution.
The first case of such a system was the “Beer engine” designed by Joseph Bramah patented in 1785. This initial design was a handpump style of disperser taking the beer from a cellar though tubing out to a tap. All the energy required for the function of the system was provided by the server/operator.
Cellar systems such as we know them today started to become popular in the latter half of the 20th century. The widespread use of pasteurization of beer to stop the fermentation process and “seal in the flavour” created the right conditions for a cellar system to be commercially viable across all establishments.
The core change to the concept of the beer engine was to have the handle where the beer flows out to be a valve or tap rather than the source of the suction from the keg. This change is thought to be the source of the phrase “on-tap”. This innovation removed the quality differences in your pint based on the server you had and created more uniformity; teaching someone the techniques for creating the perfect pint is far simpler when you don’t have to join a gym to perform the act.
This change also leads to the wider use of gas in cellar systems. When using a tap of any sort the only way it works is if there is pressure. When the fluid your chosen fluid (water, natural gas or beer) really wants to go somewhere, it is much easier to control what it does; pipes and taps are the tools that help us do that.
In order to give that fluid energy, we use compressed gas. Compressed gas wants to become un-compressed and it will push on other fluids in the system to do that. In beer gas system, nitrogen and carbon dioxide will push beer to the bottom of the keg, by doing this simple action it forces other beer up the pipe in the middle of the keg, up through the lines all the way to the tap where it flows into a glass ready for drinking.
The beauty of this is as soon as you set the pressure going into the tank the beer is ready to come out the tap, the tap controls the beer and the gas without any additional effort.
The final piece to this puzzle is how the pressurised mix of gas is responsible for keeping the bubbles in your beer. Just about everything flows in one direction; from high to low, rivers flow down mountains and cells absorb nutrients they lack from a source the other side of their walls. This basic principle is how CO2 stays dissolved in your beer, as long as the pressure stays high outside the beer the gas has nowhere to go, as soon as the pint is poured the pressure outside the beer is lower and the gas escapes as bubbles.