When dispensing keg draft beer, a key objective is to constantly maintain the brewers’ specification of carbonation (CO2) for the beer the entire keg. Any change in the CO2 carbonation level will alter the taste, pouring characteristics, and beer appearance. Most breweries in the U.S. recommend a CO2 pressure between 12-14 lbs. for ale and lager types of draft beer while in the keg at 38° F. This pressure applied to the keg will maintain the level of carbonation specified by the brewery, preventing issues.

This keg pressure is one of two pressures in a dispensing system. The other is the back pressure or “restriction” against the beer as it passes through the system. One of the three variables consisting of this restriction that has a significant amount is the beer tubing. It is used to transport the beer from the keg to the faucet and create back pressure against the beer controlling how fast or slow it pours from the faucet (flow rate). The other two variables, miscellaneous hardware, and gravity provide restriction as well.

The goal is to install the same amount of back pressure or “restriction” as is the pressure that is applied to the keg. In other words, a “balanced system” If accomplished, the flow speed of beer pouring from the faucet will be appropriate for dispensing into most types of glasses. Applied pressure to the keg, based on its temperature and carbonation, is always determined first.

Then, the inside diameter (I.D.) and length of the beer hose, hardware, and gravity are calculated to "balance" against the pressure applied to the keg assuring the beer dispensed from the faucet is neither too fast nor too slow. The more restriction added to a system, the slower the beer flows from the faucet; if the restriction is lower than keg pressure, the flow is faster.

For example, most beer towers have a 5' length of (3/16” I.D.) vinyl beer hose. This is because this size and length of tubing, in addition to the hardware and gravity, is the appropriate restriction for most keg refrigerators being dispensed with 12-14 lbs. of CO2 pressure.

In applications where the distance between the keg and faucet is greater than 5', a larger size (I.D.) of tubing, often combined with 3/16” I.D.,  should be used to balance the system. This is because 3/16” I.D. vinyl beer hose longer than 5' would cause the beer to flow too slowly where too much restriction is in the system for CO2 pressure against the keg.

To assure the best glass of draft beer Micro Matic recommends setting the CO2 pressure to maintain the brewer's carbonation specification and then controlling the flow rate with the proper length and diameter of the beer hose.

To learn more about restriction, contact one of our dispense experts or sign-up for our Dispense Institute Advanced Training Course.