Pouring the Perfect Pint

Many homebrewers prefer to package their beer in kegs rather than bottles, as it saves considerable time in cleaning and preparation. That keg then gets placed into a kegerator, where it’s pressurized with Carbon Dioxide (CO2) and served through a tap. Simple, right? It is, but there are a few things that can easily go wrong if things aren’t set up just right. Pouring the perfect pint requires the beer to be carbonated to the desired level and flow at the proper rate. This, in turn, requires a balance of temperature, CO2 pressure, and serving line length.

tl,dr: 36 ºF + 10 PSI + 10’ of 3/16” ID hose + patience = Perfect kegerator pour for most beer styles

Here’s a simple process I recommend for setting up kegerators at home:

  1. Choose a temperature for your kegerator. I usually turn the temperature pretty low, to 36 ºF, because it makes some of the next steps a bit easier. If you prefer to serve at a warmer temperature, go for it.
  2. Set your CO2 regulator so that your beer will be carbonated to the desired level, based on your preference and the temperature you’ve chosen. I usually keep mine set to 2.5 volumes of CO2, which works as a good average for the beers I make. Given my 36 ºF temperature, that means I set my regulator to about 10 PSI. I have the following chart from kegoutlet.com taped to the side of my fridge, next to my gas cylinders, if I ever want to change that: 
Temperature vs Pressure to get desired carbonation level. From www.kegoutlet.com
  1. Choose your beer line size and length so that the beer pours at a reasonable rate. Using a line that is too wide or too short will cause beer to flow into the glass too quickly and foam, making it flat. Choosing a line that is too narrow or too long will cause beer to pour slowly. I like to err on the side of caution, and use about 10’ of 3/16” ID line. Normally it pours fairly slowly, but if I raise my pressure in order to carbonate a beer to a higher level, it means I don’t need to change my line to maintain a flow rate that keeps the beer from foaming when it hits the glass. The basic rule of thumb I use is to use 1’ of 3/16” line for every PSI the regulator is set to. I’m at 10 PSI with 10’ of beer line.

In bar/restaurant applications things tend to get a little trickier, because not only are the beer lines typically much longer, but keg coolers can be located on a different floor of the building than the tap, which affects the beer flow rate. With long beer line runs that travel a large vertical distance, it’s common to use “beer gas” instead of pure CO2. This is a mixture of CO2 and nitrogen. Because nitrogen is essentially not soluble in beer, it allows for higher pressures to be used without over-carbonating the beer. There’s some science behind all that, which we’ll save for another day.

In summary, a perfect pint requires the beer to be carbonated to the desired level and for it to flow out the faucet at a slow enough rate that it doesn’t foam in the glass and lose too much carbonation. This is a balance between temperature, CO2 pressure, and line length. Temperature is based on preference, CO2 pressure is based on desired carbonation level and temperature, and line length is based on CO2 pressure.

Here are a few common problems that can be found in home kegerators and how to correct them:

  • Beer rushes out of the tap too fast, leaving a glass full of foam with little liquid: Usually either the CO2 pressure is set too high or the beer line is too wide or too short. I’ve seen a lot of commercially-available kegerators that come with about 3’ of ¼” line. That almost always needs to be replaced with a longer length of narrower line. If CO2 pressure increased for some reason (looking at you, children-who-shouldn’t-be-touching-dad’s-beer-stuff!), it’s a double-whammy, because not only will the beer flow faster, but it’ll be more highly carbonated if it had sat that way for a while.
  • Beer pours out slowly, but foamy: This usually means there are bubbles in the beer line for some reason. A common cause of this is a kegerator with a tower on top where the taps are located. If the space inside that tower is warmer than the rest of the kegerator, the beer will warm up as it sits there, causing CO2 bubbles to form, since warm beer doesn’t carbonate to the same level as cold beer, given the same CO2 pressure (see that chart above). There’s no quick fix, but sometimes using a computer fan to blow cold air into the tower space can greatly reduce the problem. Insulating the tower can also help. If all else fails, just pour pints in quick succession to reduce the time bubbles can form.  😉  The problem could also be that the beer was overcarbonated before being connected to the tap line, which can happen when trying to quick-carbonate a keg or connecting a keg which was carbonated by someone else (perhaps another homebrewer or a commercial brewery). Essentially the beer in the line has more CO2 dissolved in it than the exerted CO2 pressure can contain, and the bubbles come out of solution. There’s not a real quick fix here, unfortunately. The best thing to do is disconnect the beer line and release the pressure from the headspace on the keg every few hours until the problem is gone. If temperature differentials aren’t the problem, and the keg isn’t overcarbonated, and you can’t see any bubbles forming in the line, it could be a bad seal on the liquid line allowing CO2 to enter directly from the headspace. This usually means the o-rings on the keg fittings need to be replaced.
  • Beer is pouring at a reasonable rate, but is flat: Either the temperature is too warm (check the chart above), or the beer needs longer to carbonate. Resist the urge to raise the CO2 pressure, as this will cause the beer to flow faster.
  • Beer is pouring too slowly: When you just don’t have the patience to wait for a pint to pour, you’ve got two options: either shorten the beer line, or increase both the CO2 pressure and temperature. I usually recommend the former.

So what about actually pouring? This one is a bit straightforward. If everything up to this point is set up properly, pouring the perfect pint is as easy as this:

  1. Hold the glass at a 45 degree angle, and place it just under the faucet so the faucet is in the glass, but not touching it.
  2. Open the faucet fully and quickly. Any time the tap is partially open it will cause the beer to foam.
  3. Allow the beer to fill the glass, tipping it upright once the beer approaches the faucet.
  4. When the beer gets about 3/4″ from the rim of the glass, quickly close the faucet fully. The head should form and fill the rest of the space to the rim.
  5. Top off if needed. If there isn’t enough head on the beer, crack the faucet slightly to add some foam. If there’s enough head on the beer but the level is low, open the faucet fully.
  6. Clean your faucet. Nasty things happen to faucets left uncleaned.

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