Draught Operations > A Matter of Balance > Components of Balance

To understand and manage draught system balance, we’ll look at four measurements: beer temperature, applied pressure, resistance and beer carbonation level.

We measure beer temperature in degrees Fahrenheit. Just remember that we want to know the temperature of the actual beer. Since it takes a keg of beer many hours to stabilize at the temperature of the cooler, the beer temperature can vary quite a bit from the setting of the thermostat in your cooler. (See the section entitled “Cold Storage and Proper Chilling of Kegs before Serving” for further details.)

We measure applied pressure in pounds per-square-inch-gauge abbreviated as “psig,” or often just “psi.” The pressure applied to any keg is shown by the gas regulator attached to it.

Resistance comes from components like the beer line and changes in elevation as the beer flows from keg to glass. We measure resistance in pounds and account for two types: static and dynamic.

Static resistance comes from the effect of gravity, which slows beer being pushed to a level above the keg.  Each foot of increased elevation adds approximately 0.5 pound of resistance to a system. If the beer travels to a faucet below the keg level, each foot of decreased elevation subtracts 0.5 pound of resistance from the system. The gravity factor remains the same regardless of tube length, bends, junctions or other configuration issues. When the keg and faucet heads are at the same height, there is no static resistance and this factor has a value of zero.

Dynamic resistance comes from all the beer components in a system.  Items like couplers and faucets have specified resistance values. Beer lines provide a certain resistance for each foot the beer travels.  We have mentioned beer lines made from vinyl, barrier tubing and even stainless steel.  Each type and diameter has a different resistance (stated as “restriction”) to beer flow as shown in the nearby chart. (Note: This chart is provided as an example only. Please consult your equipment manufacturer for values suited to your beer lines and system components.)

Brewers measure beer carbonation in volumes of CO₂. A typical value might be 2.5 volumes of CO₂ meaning literally that 2.5 keg-volumes of uncompressed CO₂ have been dissolved into one keg of beer. Carbonation levels in typical beers run from 2.2 to 2.8 volumes of CO₂, but values can range from as little as 1.2 to as high as 4.0 in specialty beers.

Now that we understand the concepts of beer temperature, applied pressure, resistance and carbonation, let’s look at how they all interact in a draught system.

Next Topic: Carbonation Dynamics >