Balancing a Draft System

Today’s technical discussion for homebrewers with a draft system is the ever popular and sometimes mysterious topic of system balance. Having seen dozens, if not hundreds, of YouTube videos and online discussions, I recognize that there is a tremendous amount of bad, confusing, or simply unhelpful information out there on the subject. It sometimes hurts my head because the how and the why is not really all that puzzling. Over three pages in this column, I will explain in simple language and dismantle some of the myths surrounding draft system design. You can trust me, I am a professional (draft system installer/servicer) who also maintains multiple kegerators at home.

A balanced draft system will pour a perfect pint, with the proper amount of foam, at the proper temperature. A perfect pint is that beautiful beer that has the desired foam collar and does not waste beer. We want to get that perfect pint every time we pour with little fuss. Serving your homebrew from a bottle is cool. Serving that homebrew in a perfect pint is outstanding.

If you have ever messed around with line diameter, line length, temperature, applied pressure, or felt like you needed to change equipment in pursuit of the perfect pour, this article is for you. Let’s get to pouring the perfect pint and stop dumping foam. You worked hard for that homebrew — don’t waste it. This summary of system balance will discuss the how and the why while simultaneously describing corrective measures. I have found that most discussions about system balance don’t get into why, but are quick to tell you what you should be fixing to adjust your system. The truth is that system balance requires a simple understanding of temperature, pressure, and resistance, the rest is quite intuitive. With some patience, you can learn to identify and correct foaming issues with your draft system, starting with the most common problem. 

There are only three variables in any draft beer system: Temperature, pressure, and resistance. In that order. That’s it, and it means you only need to think about three possible issues to address when your pours aren’t right. Your system might need corrections to one, two, or all three variables, but once you know how each variable affects your draft beer, the needed changes are not very difficult.

Think of system balance as a three-legged stool. Each leg is equally important, and if one leg is out of whack you do not have a solid seat. When all three legs are adjusted accurately, the stool is stable. 

Temperature

Temperature problems make up the majority of draft-related headaches. Fortunately, it is also the easiest to diagnose and cure. First, the beer in the keg should be at 38 °F (3 °C) and the beer in your glass should be the same temperature. If you find that the beer in the glass has warmed by even one or two degrees, you will be pouring some foam. If you like your draft beer warmer than 38 °F (3 °C), well, things are going to get much more difficult. You want a perfect pour? Then 38 °F (3 °C) it is. A degree or two colder won’t have a significant impact, but a few degrees warmer and things can get squirrelly. It is not impossible to get a good pour at 44 °F (7 °C) (with additional pressure and more line restriction to balance the system), but since you are presumably reading this because your system is not perfect, let’s try to get a good design at 38 °F (3 °C) before we start experimenting.

Place a glass of water inside the kegerator and leave it alone until the temperature stabilizes. Use a quality thermometer and measure the temperature. Compare it to the temperature of the first 3 or 4 ounces of poured beer. If you are off by a few degrees, it indicates that the beer in the line is warming. We need to correct that problem and it might require a fair bit of homebrew ingenuity.

The colder the liquid, the more dissolved carbon dioxide (CO₂) the liquid can hold. That is dissolved CO₂ gas, before it has become foam. The dissolved gas will break out of solution in the beer line and then you’ll have a slug of foam as you open the faucet and pour. The foam will rise to the highest point in the line. If you have a quick burst of foam followed by clear beer, your warm spot is near the faucet. If you have clear beer, a bit of foam and then clear beer, the foam is rising to a bend somewhere in the beer line. If you pour some foam and then consecutively pour perfect pints, surely it is a temperature problem occurring after the keg.

Identifying temperature-related foam is not hard, but correcting the problem can sometimes be a chore. As we have determined, we need to maintain a constant temperature from keg to glass. In practice this is not always possible to execute to perfection with a home draft system. But we can get very close to perfection. First thing is to be sure all gaps are sealed in the refrigeration unit. Place a bright light inside the kegerator, close the door and turn off the lights. Look for light leakage. Seal those however you can. Next, be certain your draft tower is sufficiently insulated. It is not uncommon, or even a problem, when the tower sweats. That is water vapor condensing on a cold surface. If you have a lot of sweat on your draft tower, it’s because the metal tower is absorbing ambient heat. The line in the tower is likewise gaining some heat. Well-placed insulation can help. I caution, however, don’t overdo it. Dumping a can of spray foam in the draft tower is not a solution because we are going to want to cool the tower, and that requires air flow.

Higher-end kegerators will always have a fan and tube assembly to get cold air into the draft tower, all the way up to the faucet. Be sure the fan is working and that the tube is extended all the way up into the draft tower (it is a costly service call to show a client where that dangling hose is supposed to live). If you don’t have a fan, fear not because the fine folks at Amazon (and other retailers) have you covered. A small fan with 20 to 50 cfm is plenty. More than that, and you’ll start to force air out of the gaps you carefully sealed. Place the fan near the cooling coil, if possible, and direct the tube all the way up to the shank. Now you have a top-of-the-line kegerator. Congratulations. Cooling the tower is not just important, it is required if you want that first pour to be as good as the second. The cold air from the kegerator is not going to rise up to the faucet and shank on its own, and you will have foam if you do not keep the beer within the tower cold. The tower fan can fix it. 

Next thing to consider with temperature, though it is unlikely, is you may have a problem maintaining keg temperature. Cheap refrigeration units feature cheap parts and that includes the internal thermostat. If the factory set cut in/cut out temperature variable is too large, it is possible that the keg is not holding a consistent temperature. This is especially true when a keg gets to the last few pints. The liquid will gain heat faster than it will chill down. If your compressor is not cycling enough, the keg might be warming and releasing CO₂. An outboard thermostat will fix this. It might also burn out the compressor prematurely, but that is the nature of a cut rate appliance. If your keg is not maintaining temperature, surely your draft tower is not either. 

So that’s temperature. By far the most important variable but also the easiest to fix and diagnose. Before moving to any other corrections, be certain that beer temperature is sorted.

Pressure

Foam is not often caused by too much applied pressure; instead it is often a result of too little applied pressure. How is that possible? Relating that dissolved CO₂ is gas that remains within the liquid and foam is gas that has escaped from the liquid as it equilibrates with atmosphere, we want to be sure the dissolved CO₂ content is maintained from keg to faucet. If your keg of beer has 12 psi of pressure applied at 38 °F (3 °C) you will eventually achieve 2.6 volumes of carbonation. As you are now maintaining temperature, you should be maintaining applied pressure. 

Here is the rub: It is tempting to adjust the applied pressure to fix foaming problems. There are two convenient knobs. One is the thermostat and the other is the regulator. 

Hold on. Adjust the temperature and you are messing with one of the legs of the stool. We need to hold 38 °F (3 °C) first and foremost. Lower the applied pressure and now you have gas escaping from the beer in the keg, and also in the beer line. The keg doesn’t end at the coupler or quick disconnect after all. The beer doesn’t know it’s all one big system until it is poured into your glass. Now you have foam. 

The next thing is to overcorrect and dial it back. Then, when we still have foam, we overcorrect and apply additional pressure. There is no immediate effect, but eventually the beer absorbs too much gas and your resistance is out of balance. 

One more reason to diagnose temperature first: I think homebrewers can really up their game by dialing in proper carbonation levels, so adjusting pressure outside of the ideal range shouldn’t be the first solution. Along with malt, hops, yeast, and water, CO₂ gas is incredibly important but too often neglected. If you have not approached how to establish and vary the CO₂ volumes in your beer, I think you’ll be very satisfied with the results once you do. And once you do, you know to maintain the volumes in your draft system. If you feel the need to nerd out about volumes and applied pressure, check out this previous “Advanced Brewing” column “Gas Dynamics” from the November 2023 issue dedicated to your regulator: www.byo.com/article/gas-dynamics

Resistance

Resistance is one and done. When you have it right, you will not need to adjust resistance again. Resistance is simply the sum of friction from the keg to the glass. Here is a quick analogy to help us understand resistance. The spigot on the side of the house will blast water when fully open. Attach 100 feet (30 m) of garden hose to the fully opened spigot and you’ll see that the flow rate at the hose end has been significantly reduced. That is because the friction in the hose slows the rate of discharge. 

We want our draft system to have the appropriate resistance; neither too much nor too little. A balanced system is just that, meaning all three variables are working together and delivering the perfect pour. The thing with resistance is that we can’t easily change it up like we can with pressure or temperature (but there is a hack only available to homebrewers, which is necessary when pouring beer styles at different carbonation levels, which I will get to later).

The usual draft system, a kegerator or keezer, requires a certain length of choker. Choker is an appropriate term, because it chokes the rate of flow from keg to glass. With no choker, the beer will spew out at a rate equivalent to the applied pressure. Beer that pours at 12 psi is coming out like a firehose and impossible to tame in the glass. Chokers in America are universally 3⁄16-inch inner diameter and usually 7⁄16-inch outer diameter (check out a deeper dive into tubing in my previous article “Choosing Tubes and Hoses” at www.byo.com/article/choosing-tubes-and-hoses). You’ll need to know the specific resistance of your choker. It will be between 2.2 psi and 3 psi. This is important. If your supplier can’t tell you the resistance per foot, keep looking because it is the most important and only important variable we are working with. 

Let’s assume we have the best available, thermo-plastic extrusion (TPE) choker. This is free of BPA and phthalate, and oxygen impermeable as well. It will have a resistance of 3 psi per foot. A keg with 12 psi of pressure will require 4 feet of this tubing to be balanced. But we also need to consider the shank, faucet, and coupler, so add around 1⁄2 psi of resistance. Therefore, our 12-psi keg needs 12.5 psi of resistance, or 4.2 feet of TPE tubing. Finally, gravity adds resistance. Precisely 0.45 psi per foot of lift. Round this up to 0.5 psi. Measure from the middle of the keg to the shank and add the appropriate resistance. We need about 13 psi of resistance in this theoretical set-up. 

Now, here is where we can let loose a little bit. Because in theory, a balanced system is ideal. In practice, your home bar is not serving pint after pint all night long. We can relax a few extra seconds while the beer pours, and a few extra seconds makes a huge difference. You really don’t need to pour a pint in eight seconds, but you really do want to take a moment to get a great head on that beer while not dumping any at all. So let’s add a few pounds of resistance. I like to see eight- to ten-second pours on commercial systems. Eight seconds is beneficial at a busy sports bar, and dumping a little is sometimes OK in the name of speed. An evenly balanced system will pour a pint in about eight seconds. Ten seconds is more profitable for a craft bar when the kegs cost serious money and the customers expect a nice pour. A home bar can go to 15 psi of resistance without any problems, and allow for a much better controlled pour with a great presentation. The speed of the pour affects foaming in the glass. It is hard to tame the beer when it is flowing too quickly.

Now, about that resistance hack for beers intended to be poured at different carbonation levels that I mentioned earlier. We can change our choker fairly quickly. Simply install a few John Guest quick disconnects at the coupler and before the shank. Fabricate a few different lengths and you can go from 12 psi of resistance to 18 psi of resistance quickly. Or any resistance. This is helpful when trying to pour beer styles that require high volumes, like a Belgian golden ale or a hefeweizen.

Before we move on, I know what some of you are asking. “What about flow control faucets?” Simple. If your system is out of balance, flow controls will pour foam slower. The CO₂ does not stay in solution because we installed flow control faucets. If your foaming is caused by velocity — that is the beer is hitting the glass too hard — correct your pouring technique. Flow controls can help in this situation, but you probably should first reconsider the amount of system restriction.

So those are the three variables, and you can see it is not all that difficult to get a balanced system. If you are ambitious and want to explore designing and installing a complex long-draw system, I covered that topic in the December 2022 issue, online at: www.byo.com/article/long-draw-draft-system.

Written by Bill Jablonski