How a Draft Beer Pressure System Works

Draft beer pressure is an integral part of the operation of a draft beer system. For your draft beer, using it properly and controlling it make the difference between perfect pints and problem pints.

Let's look at what you're dealing with in your draft system.

Every beer has a brewery prescribed amount of dissolved Carbon Dioxide. This dissolved gas is called carbonation. Carbonation is important to the flavor and texture of the beer. It is part of the beer, but it also causes problems and confusion within a draft beer system.

Brewers measure the carbonation in relative terms as “volumes of CO2.” A brewer might refer to a beer as having 2.8 volumes of CO2 dissolved in it. That means that for every volume of liquid beer there are 2.8 volumes of CO2 dissolved. The “volume” could be any pre-determined value such as cubic inches.

The correct carbonation can be achieved either from natural fermentation (known as cask or bottle conditioning) or by forcing CO2 into solution using pressure (referred to as force carbonating). The temperature of the beer is a major factor in the amount of CO2 dissolved because the colder a beer is the more CO2 can be dissolved in it. So to further define his or her beer, a brewer would say the beer has 2.8 volumes of CO2 at 38 degrees Fahrenheit - 38 degrees Fahrenheit being the optimal serving temperature for most ales and lagers.

Learn more about carbonation.

When dispensing the beer via a draft beer system the goal is to maintain the brewer’s specified carbonation level all the way from the keg to the glass. To achieve this goal you have three variables to work with: temperature, system resistance and applied draft beer pressure.

Beer storage temperature is vitally important and the systems in place for this are a subject of another discussion. So that leaves us with the pressure as one variable that can be altered. The third variable is the resistance applied to the beer by the draft system itself as the beer travels to the faucet.

Resistance can be difficult, but not impossible to alter. In direct draw and kegerator systems, resistance can be changed easily. However, in most long draw draft beer systems the resistance is buried within the installation and changing it is difficult.

Applying draft beer pressure to your system has two purposes (1) to maintain the carbonation of the beer in the system and (2) to push the beer through the system from the keg to the glass. Here is where a lot of confusion starts and there are important points to remember when pressurizing your draft system:

1. You have to take into account the brewer’s intended carbonation level. For most beer that is going to require an applied pressure of between 12 and 14 pounds per square inch (PSI)at 38 degrees.

2. There will always be a certain amount of “back” pressure or resistance applied by the draft beer lines, gravity, keg couplers, faucets and other devices or fittings in the beer system.

3. The longer the beer lines, the more resistance is presented to beer as it flows to the faucet. Furthermore, the smaller the diameter of the hose, the more resistance it applies.

The type of draft beer system you are working with and the overall resistance that system applies to the beer is the key factor determining the gas pressure to be applied. In most cases you are either working with a “Direct Draw System” which has the kegs in a cooler directly below, behind or alongside the faucets. Or you will have a “Long Draw System” where the kegs are stored in a cooler that is in a remote location from the faucets.

Pressure in a direct draw system
Pressure in a long draw system

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