Proper balancing of a draft system is key to excellent presentation and serving of your homemade and commercially produced beverages. The most common side effects of an unbalanced draft system are overly foamy pours or slow pours. Err on the side of too much restriction, as a slow pour is better than a foamy one. Proper balance is determined by the pressure your beer is at, and the resistance (in units of pounds of resistance per foot) on the system. Resistance is provided by a couple of variables; we will talk about the most prevalent, tubing and elevation change. We’ll assume a keg pressure of 12 PSI, you may want to change that based on your desired carbonation rate.
Most home draft systems use 3/16” ID vinyl beverage tubing, which has a restriction of 3 pounds per foot. To achieve balance with your beer at 12 PSI, use 4 feet of 3/16” tubing (4 feet x 3 PSI per foot = 12 pounds of total restriction). For beer at 15 PSI, you would use 5 feet of 3/16” tubing.
¼” tubing has a much lower restriction than 3/16”, at .85 pounds of restriction per foot. For beer at 12 PSI, it would take 14 feet of tubing to get the same amount of restriction that you would for 4 feet of 3/16.
Gravity has an important impact, the above examples do not take into account the affect of elevation change with your beer. One foot of upwards elevation change imparts a half pound of restriction. Going downwards decreases your restriction by .5 pound per foot. If your draft system goes up 6 feet before serving, and you had your keg at 12 PSI, you would need 10.5 feet of ¼” tubing. If you were going down 6 feet, you’d need 5 feet of 3/16” ID tubing.
A little bit of multiplication can save you a lot of trouble when all you want is a perfect pint from your taps. For further information, please visit www.draughtquality.org