Thanks  to James C Neu of DraftMore for this great information on CO2 and beer.

The carbonation level of the beer is determined by the brewer to match the style of the beer.  Generally speaking, ales and stouts are designed with lower levels of carbonation, whereas lagers are generally carbonated at higher levels.  At higher levels, CO2 has a noticeable flavor (carbonic acid), and the taste, as well as the aromatics from the head are part of the overall flavor profile.  Over or undercarbonated beer is not only messy and wasteful, it also diminishes the taste and experience the brewer designed.

Beer is delivered from the brewery properly carbonated.  In the U.S., carbonation levels are described in volumes of CO2.  So, if a beer is described as being a 2.4 volume CO2 beer, it has the equivalent of 2.4 x the container volume of CO2 dissolved in the beer.  This is possible because the container is under pressure – the correct amount of pressure keeps the CO2 dissolved in the beer.  When the beer is in equilibrium, the same amount of CO2 is leaving the beer as is dissolving into the beer.   This is a constant process.

In a sealed keg, the amount of CO2 is fixed, so colder temperatures will result in more CO2 dissolving into the beer, whereas warmer temperatures cause CO2 to come out of the beer faster than it dissolves.  As long as the beer does not get too warm for a prolonged period, and is properly cooled before serving, the beer will reach equilibrium again.

A properly adjusted regulator keeps the beer CO2 levels in equilibrium.  If the temperature is correct and constant and the pressure is correct and constant, the keg will serve well to the end.  If the temperature changes while the pressure remains constant, under or overcarbonation will occur, and if the differences are too great or occur over too long a period, the beer will be ruined.

SYSTEM FUNDAMENTALS

In order to serve a properly carbonated beer, a dispensing system must be set up properly.  There are three main parts to proper system design, all of which are interrelated – pressure, temperature and restriction (flow).  A system which always results in a properly carbonated beer at the correct temperature is called ‘balanced’.

Per Boyle’s law, pressure, temperature and volume are interrelated.  Since the volume of the container (keg) is fixed, we only have to worry about setting the pressure and temperature correctly.  American draft beer is not pasteurized, one of the reasons many people prefer the flavor of draft beer to packaged beer.  Because it is not pasteurized, draft beer cannot be stored for any length of time over 42 degrees F – it will spoil.  Ideal storage temperature is generally considered to be 38 degrees, but 36 – 38 is considered an acceptable range.  If you prefer warmer beer, it is recommended that you warm you glass slightly before pouring a beer.

The temperature target is a liquid temperature measurement (one way to check is to take the temperature of the second beer out of a keg).  Once the target temperature is reached, the temperature should be maintained as evenly as possible.  This is important because the temperature of the beer and the carbonation level of the beer determine the proper regulator setting.  If the temperature changes by more than 2 degrees F, the regulator pressure must generally be adjusted by 1 psi to keep the beer in equilibrium.  The problem generally lies in keeping up with the temperature changes (the temperature which matters is the temp in the center of the keg, called the core temperature).

REGULATOR SETTING

The purpose of the regulator is commonly misunderstood.  Simply put, the job of the regulator is to deliver the right pressure to maintain the carbonation level of the beer.  If the temperature and the carbonation level of the beer are known, the proper regulator setting can be determined by consulting an equilibrium chart.  The setting shown by the equilibrium chart will keep the beer from becoming over or under carbonated.  If the regulator pressure is higher than equilibrium, CO2 will dissolve in the beer, raising the carbonation level and creating a new equilibrium.  However, this will change the character of the beer, and will often result in foamy beer.  You can safely add up to 1 psi push pressure to ensure good flow without causing problems.

For every 2,000 feet of elevation 1 psi of regulator pressure must be added to compensate for lower atmospheric pressure.  Regardless of the higher regulator setting, flow will be the same as at sea level, as the total pressure (atmospheric + regulator) will be the same.

Once you have your regulator properly set, you need to determine the length of the restriction hose and account for the lift, the drop and the restriction of the fittings.  Generally, restriction hose offers resistance between 2 – 3 lbs per foot.  Most direct draw kegerator systems are supplied with 5 feet of restriction hose, but proper restriction is usually best determined by experimentation.  Starting with about 7 – 8 feet of hose, you can remove 4 – 6 inches at a time until the flow is correct.  Never adjust the regulator for flow, you will screw up the beer.

You will know you have your system set up properly when the last third of the keg pours properly.  This is when problems show up – overcarbonated beer will be all foam, undercarbonated beer will be flat (having been somewhat foamy for the first two thirds of the keg).

Nearly all secondary regulators for beer systems are functionally the same.  Spending more for a premium regulator will buy you upgraded internal parts and a nicer body with better plating for longer service, but not necessarily better accuracy.

Regulators used in the beer industry are supplied with inexpensive gauges which are not very accurate.  Most draft service professionals will tell you they don’t trust secondary regulators, and they often use a pressure tester with a more accurate gauge to determine what pressure the secondary regulator is really delivering.  In our testing, we have seen secondary regulators, even new ones be off as much as +/- 3 psi.  It is not common to be off this much, generally it’s +/- 1 – 1.5 psi.

Without a regulator test device, you may have to experiment with regulator settings to find equilibrium.  One easy way is to turn the regulator down to about 5 psi and tap the keg.  You will see bubbles collect in the high spots of the line because the regulator pressure is too low, and CO2 is coming out of the beer.  Turn up the regulator pressure until you no longer see bubbles in the line.  Add about 1 psi for serving pressure and you should be good to go.  Once you find the right equilibrium setting for a certain beer, you should not have to change the pressure unless you choose a different target temperature or you change to another type of beer.

DRAFTMORE REGULATORS

DraftMore Automatic Regulators are just being introduced to the US market, though over 20,000 units have been sold worldwide.  DraftMore regulators differ from standard regulators in several ways.  A DraftMore regulator contains a Swiss made precision needle valve for precise metering, resulting in a much more precise regulator (+/- 0.25 psi).  It is also a sealed regulator, so it is not affected by atmospheric pressure changes or by elevation (unlike a standard regulator).  But the most innovative part of the DraftMore regulator is its ability to adjust to temperature and maintain equilibrium at all times.

DraftMore regulators have a bellows which contains a mixture of gases.  These gases expand and contract in response to temperature changes, pressing harder or less hard on the needle valve.  The bellows expansion is countered by the pressure from the keg.  The DraftMore regulator attaches directly to the gas port of a keg coupler, so that it responds to beer pressure and  temperature as beer goes through the coupler.  Once the pressure reaches equilibrium, the DraftMore regulator shuts off until either beer is served and more CO2 is needed, or the equilibrium point goes higher than the level in the keg due to temperature changes (for example in a frequently used walk in cooler).

Because of their high precision and ability to maintain keg equilibrium at all times, DraftMore regulators offer a unique solution to regulator problems and improperly carbonated beer.  There is nothing to adjust on a DraftMore regulator, so you can’t set it incorrectly.  DraftMore automatic regulators come with a 3 year replacement warranty because we believe they are the best regulators you can own, and they will save you money and beer in a short period of time.  We have seen savings of between 7 – 15 more glasses of beer per keg.  Please contact jamescneu@draftmore.com or visit www.draftmore.com for more information.