This article is meant to help anyone who is serving beer on draft---homebrewers and non-homebrewers alike. You will learn how to carbonate beer, the factors that affect beer carbonation and how to manage them to achieve your desired carbonation level. Additionally, you will learn about keg line balancing to create the correct amount of resistance in the beer service line to avoid foaming while pouring.
Learn. Make. Share. Repeat.
Editors Note: If you are new to kegging, you should first read our introduction to kegging article linked below.
Whether you are setting up a draft system or just giving it a tune up, this guide is for you. Homebrewers can use this article to carbonate their beers and balance their lines. Casual beer drinkers or servers can use this article to prevent the dreaded foamy pours. But this article is not just limited to beer and beer drinkers. This article can be used for draft ciders, carbonated water, sodas, carbonated kombucha, and even sparkling wines. Though the beverage may change, the principles and techniques are the same. By understanding the five basic factors that affect a draft system, we should be able to bring all things into balance and produce the perfect pour.
First, before going any further in this article, it is important to understand that if you have a leaky draft system, NOTHING WILL FIX YOUR PROBLEMS UNTIL YOU ARE NO LONGER LEAKING. Please, if you have not pressure tested your system, stop here and check out our “Pressure Checking a Draft System” blog first. It is important that you not only pressure test your draft system, you should also pressure test your homebrew kegs as well.
Now that we have a leak-free draft system, let’s get on with carbonating the beverage and balancing the system.
The Factors - Temperature, Volumes of CO2, PSI, Draft Line Resistance, Time
There are five major factors that come into play when balancing your draft system.
The first factor is temperature and it is where I would recommend you start. There is no perfect temperature for serving draft beverages. What temperature do you like to drink your beer? This is YOUR kegerator. Whatever temperature YOU like to drink beer, that is the temperature you should be setting YOUR kegerator to. Personally, I like my beer cold as ice. I run my kegerator at about 36° F.
Joe’s Pro Tip #1: Even if you like your beer just above freezing (water freezes at 32° F), most temperature controllers have a range of degrees above and below the set temperature before the compressor will kick on or off. This is known as the operating differential. I used to keep my kegerator at 33° F, but the beer in the lines would freeze from time to time, so I had to raise the temperature a little to account for the controller. Know and account for that range for your controller before choosing a temperature.
When we talk about temperature, we are talking about the actual temperature of the beer (the LIQUID itself, not the air temperature). Most temperature controller probes by default measure the air temperature in the fridge. The temperature we care about is the temperature of the liquid: liquid temperature directly affects the ability of that liquid to retain gases in solution. The warmer the liquid, the lower its ability to retain carbonation. So, the warmer you get, the harder it is to keep a keg carbonated. Remember, at room temperature, gases want to be gases, even if they are trapped in your keg.
Joe’s Pro Tip #2: If you have a waterproof temperature probe for your controller, you can place it into a cup of water in the fridge to get the controller to work off of liquid temperature. Alternatively, you can use LCD temperature stickers directly on your kegs to see the actual liquid temperature inside. They work very well. Just make sure you clean and dry the surface before applying them or they peel off.
Liquid Crystal Display Stickers read temperature accurately through the keg wall.
Volumes of CO2
The second factor is Volumes of CO2. Volumes of CO2 is just that, the volume of CO2 that you want to force into solution in the beer. So, what we are really talking about is: how carbonated do you want your beer? Higher volumes mean more carbonation. Let’s take a 5 gallon ball lock keg as an example. If you wanted to carbonate 5 gallons of beer to 2 volumes of CO2, you will need approximately 10 gallons of CO2 (a 2:1 ratio of CO2 to beer). So how many volumes do you want? This is really 'dealer’s choice'. Do you like highly carbonated beer? Do you prefer barely carbonated beer? Most beer around the world is carbonated to between 2-3 volumes of CO2. American beer is typically carbonated a little higher---typically somewhere between 2.5 - 2.8 volumes of CO2 to beer. British beer is lower generally around 1.8 - 2.2 volumes of CO2 to beer. Ciders are usually around 3 volumes. Carbonated waters and sodas are generally around 3 - 4 volumes. Traditional French champagne is carbonated to 6-6.6 volumes, but sparkling wines are nice between 2.5-4 volumes. It's within your control, you can make the carbonation any level you like.
Joe’s Pro Tip #3: Personally, I like my beer pretty carbonated and generally run 2.8 volumes for most of my beer. I like my carbonated water around 4 volumes. Ciders and sparkling wines I generally run around 3 volumes.
As you dissolve carbon dioxide into a liquid, it forms carbonic acid. Carbonic acid gives soda that burn in your throat when you drink it too fast. In beer it tends to make beers come off crisper, sharper and more acidic. As you increase the carbonation level, you are also increasing the level of dissolved carbonic acid. This could shift the balance of the beverage you are serving. If a beverage comes off as too sharp while tasting, you may want to lower the volumes of CO2 and therefore the corresponding carbonation level.
Pressure in PSI (Pounds per Square Inch)
To figure out the third variable, PSI, we need to use a carbonation chart. A carbonation chart brings the first three variables together in one place and shows their relationship. Start with the temperature you chose earlier. Trace that row across until you hit the desired volumes of CO2. Then trace the column up until you get to the PSI parameter. Based on the temperature of your liquid, and the desired volumes of CO2 you want the beverage to be carbonated to, the chart will reveal the required PSI to produce that carbonation level at that temperature.
This chart is excerpted from the homebrewing guide written by our company's founder: Brewing Quality Beers by Byron Burch.
An example: Let’s say I want my beer at 36° F with 2.6 volumes of CO2 (pretty standard). If you start with 36° F, trace across until you hit 2.6 volumes, and trace up to PSI you end up at 11 PSI. That PSI is what you will set on your regulator.
Draft Line Resistance - Diameter, Material, and Length
The next factor we need to determine is line length. The tubing performs two major functions in a draft system. First, it transmits the beverage from the keg to the faucet and into your glass. Second, it provides resistance in the form of friction on the beverage to prevent the pressure from turning into foam. In the line, there is nowhere for the carbonation to escape. Once the beer exits the line, excess CO2 pressure will be released as foam. Without the tubing keeping the carbonation in the liquid solution, it tries to escape back into gaseous form again.
The keg pressure needs to be matched from the keg to the tap with resistance from friction in the tubing. We get resistance by reducing the flow rate either by making the diameter of the tubing smaller or the length longer. You can check the chart below for common diameters, materials, and their corresponding resistance. So, if we have positive 11 PSI from the regulator, we need negative 11 PSI of resistance in the line to end up with zero pressure when it hits the tap. If the pressure is higher than the resistance, let’s say 11 PSI from the regulator and negative 9 PSI from the tubing, when the beer hits the tap it will release the excess 2 PSI as foam. It is normal to see a bit of foaming for the first few pints of a new keg once you first tap it. But it should go away as your keg acclimates to your kegerator conditions. If you are getting foam a few days into serving your keg, your lines may not be long enough to provide adequate resistance for the PSI you are running.
Line length is based on two variables: the tubing’s internal diameter and the tubing material. Since the diameter of the tubing determines the resistance, your line length will change with line diameter. Small diameters produce more resistance per foot, resulting in shorter line lengths. Larger diameters produce less resistance per foot, resulting in longer lengths which are more common in commercial operations. When your keg storage is in the back of the brewery, but your taps are in the front public house, you are going to need long lines to transfer the beer. Therefore, you increase the diameter of the tubing. But at home, generally the keg is in the fridge and the tap is within a few feet of the keg. At home we want short lengths of tubing because the tubing would just get in the way if it were long.
The table below lists common line materials and diameters.
Resistance - PSI per ft of material
|Vinyl (thick walled)||3/16"||2.7|
|Vinyl (thick walled)||1/4"||0.7|
|Vinyl (thick walled)||5/16'||0.17|
|Vinyl (thick walled)||3/8"||0.11|
|Ultra Barrier Silver™ Antimicrobial||3/16"||2.2|
The diameter and length of the tubing on the BEVERAGE side affects how the beer is served. At home, the standard sizes are 3/16” for the beverage side and ¼” for the gas side, but you could use 3/16” for both sides if you choose. Commercially, the sizes are generally a bit larger with 5/16” often used for the beverage side and 3/8” for the gas side. Please note that the gas side’s line diameter and length do not affect service at all. The gas line can be as long or as short as you like because gases will fill any volume you give them.
Joe’s Pro Tip #4: Keep it simple! I use 3/16” thick wall vinyl for both my beverage and my gas side. I don’t mind heating up the end of the tubing in some hot water to stretch it over the 1/4” barbs. In fact, I like the redundancy of tight fitting tubing and a hose clamp to help prevent leaks.
An example: To calculate how long the tubing must be to prevent foaming, divide the PSI calculated earlier by the resistance of the tubing being used. So, back to our example above of 36° F, 2.6 volumes of CO2, and 11 PSI. Let’s say we choose the standard tubing of 3/16” thick wall vinyl tubing with a resistance of 2.7 PSI per foot. Take the 11 PSI and divide by 2.7 to get 4.1 feet. It’s that simple. If we used the same parameters but ¼” thick wall vinyl tubing instead, we would need 15.7 feet of tubing!
I recommend sticking with smaller diameter tubing.
Joe’s Pro Tip #5: I generally like to add an extra ½ foot of tubing to whatever I calculate the required tubing length. If I need 5 feet, I like to take 5.5 feet. I find that the extra half foot of tubing gives you a little more wiggle room to deal with some of the assumptions we are making.
Carbonating beer takes time. It is not as simple as putting your beverage in the keg, setting the regulator, and WHAM you are carbonated. It takes time for the carbon dioxide to dissolve into the liquid. Generally, it takes about 3 days to carbonate a normal strength beer. As you increase the volumes of CO2, carbonation takes longer. When I make my carbonated water at 4 volumes, it generally takes about 5 days to fully carbonate.
There are a lot of tricks on the internet for carbonating faster. Personally, I think 3 - 5 days to carbonate is really fast, especially when compared to 2 weeks for bottle carbonating. But for some people that is just too long. Most of these tricks involve cranking the PSI of your regulator up really high for some period of time and then dropping the PSI to normal serving pressures. After reading this article you should be able to figure out why these tricks are not very effective. They often result in overcarbonated beer with lots of serving problems. Then you have to spend the next week redialing everything in. I have seen this situation here at our shop over and over again. I cannot stress this point enough. Don’t do it! You will only waste gas and make the balancing take longer. Again, three days is pretty quick. A diffusion stone hooked up to the gas side of your keg will reduce the waiting time. They typically have 0.5 - 2.0 micron holes. The tiny bubbles produced have a lot of surface area and dissolve into the beer super fast. The diffusion stone method is highly effective and rarely takes more than a day and a half to fully carbonate.
Joe’s Pro Tip #6: Personally, I have found shaking the keg while the gas line is hooked up to it to be an effective way to speed up carbonation. As you shake the keg, you splash the beverage into the carbon dioxide. This helps dissolve the gas into the beer. I have been able to get kegs carbonated in about 24 hours under standard kegerator conditions. Shake the keg every hour or so for the full 24 hours. Try it. It works and you do not have to adjust anything, just add a little elbow grease.
Final Note about Maintaining the Balance
As we discussed earlier, the temperature directly affects how much CO2 can dissolve into a liquid. If you carbonate a beverage at a certain temperature, volume of CO2, and PSI and then change the one of the variables, the whole balance will shift. For instance, let’s use our example from earlier. If we carbonate a beer to 2.6 volumes at 36° F and 11 PSI and then we take the keg out of the fridge, the keg will start to warm up. As the liquid temperature increases, it’s ability to retain the carbonation drops and the carbonation level decreases. The CO2 migrates out of the liquid and into the air space in the keg. This makes the effective headspace PSI higher than it is supposed to be. Not only will this result in lower carbonation beer, but the extra pressure in the headspace propels the beer through the line with more force resulting in foam. If the keg we used in the example above warmed up from 38 to 48° F, even though the PSI stays the same the volumes of CO2 goes from 2.6 to 2.05 volumes. That is a substantial change in carbonation level.
To maintain a steady carbonation level and a perfect pour, you need to always consider the impact that a change in one factor will have on the others.
All Things in Balance - A Recap
In summary, achieving perfect balance in your draft system really is as simple as five steps.
Addressing Rise and Fall
Before we end this balancing act, I would like to address the issue of rises and falls in height. The height difference between the height of the keg and the height of the tap can affect line balance. If beer has to travel upwards, it gains resistance because it fights gravity. When beer travels down, it looses resistance because of the aid of gravitational acceleration. Therefore, the higher you go, the less line you need. The lower you go, the more line you need. There are complicated formulas that really dial this topic in. However, if you look at the effects of rise, the actual effect is negligible for almost every home circumstance.
An example: If we use the same variables from the previous examples, and we account for no change in height, we should need about 4.1 feet of line. If we account for a 2 foot rise in height, the required line length to balance becomes 3.7 feet. This is the most that most home kegerators will deal with and it only decreased the line by 0.4 feet. If we exaggerate the issue and make the rise 5 feet (which would probably never happen at home), the resulting decrease in line length required is 0.9 feet. So even if we make a 5 foot change in height, the resultant change in line length still isn’t even a full foot! Since height has a more or less negligible affect on line length under normal home conditions, don’t waste your time with the calculation. Add the extra half a foot of line and call it good.
Copyright by The Beverage People, Inc. April 2022.