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How to get the perfect pint. Balancing your CO2 pressure and line length
It can often be a challenge to get the perfect pour from your home draft system. It can be frustrating pulling a pint of foam, but hopefully armed with a bit of information, you can get the perfect pint everytime.
There are several factors that effect how your beer will come out of the tap, some obvious like the PSI on your co2 and the serving temperature, to other less intuitive ones such as the thickness of your serving line. The essential controlling factors boil down to pressure and resistance.
Keg PressureThis dictates how much CO2 is being applied to your beer, and when taken with the beer's temperature, will determine the overall CO2 volumes dissoved in the beer itself.
Beer TemperatureThe temperature of the beer determines how much CO2 will be absorbed. The colder the temperature, the more CO2 will be dissolved.
Tap line diameterThe diameter, and rigidity of the serving line effect the amount of resistance placed on your beer as it is poured. Wider, or less rigid lines will allow your CO2 to escape the beer as it flows. Too narrow lines will inhibit your beer flow, causing too much resistance. This could reduce your pour rate to a trickle (1 Gallon/min is generally considered ideal).
Tap line lengthMuch like the diameter, the length of your line dictates how much resistance is placed on your beer as it is dispensed. While 1 foot of 3/16" ID line adds 3 PSI of, 10 feet would offer 30 PSI, making a dramatic difference in the required pressure to dispense properly.
Tap line temperatureWarmer lines will warm the beer that flows through them, pushing CO2 out along the way, causing more foam in your glass.
Height difference from tap to kegSince we're trying to balance pressure vs. resistance here, we must also take into account our old pal gravity. Thanks to gravity, the difference in height between the tap and the keg can add, or subtract resistance to our equation. Approximatly 1/2 PSI per foot, to be exact. So, if your tap is 2 feet above your kegs, you would need to account for an additional 1 PSI in your serving line's resistance. Conversely, if your kegs are 2 feet above your taps, you would subtract 1 PSI.