Draft Beer Systems 101

Draft beer systems may seem somewhat complicated at first glance. But once you tackle the basics, you’ll see that they’re actually quite easy to understand. From keg pressure settings and standard definitions, to keg dimensions and pouring techniques, we’re here to tell it all. Quench your thirst for knowledge and become a smarter, more educated draft beer connoisseur.

Glossary of Draft Beer Terms

Draft Beer

Any type of beer that is drawn from a large vessel. Kegs aren’t the only “vessels;” the term “draft beer” includes cask ale as well.


Metal container used for storing and dispensing pressurized liquids. A single hole centered at the top of the keg and a two-way valve allows liquids to be added and removed from the keg.

Keg Beer

Unpasteurized beer that is dispensed from a keg using gas pressure.

Direct Draw Draft System (Standard Draft System)

Technical name for specialized equipment built specifically for dispensing keg beer from a temperature-controlled environment through the use of compressed gas. Direct draw draft beer systems may be housed in a kegerator, walk-in cooler, or converted refrigerator.

Keg Volume and Dimensions

Note: These measurements apply to standard US kegs. US keg dimensions may vary slightly by manufacturer and brewery. European kegs vary in size, but are similar to US sizes.

½ Keg
Holds 15.5 gallons – approximately 165 12-ounce bottles
Weighs 161 pounds when full
24″ high with a 16″ diameter

¼ Keg
Holds 7.75 gallons – approximately 82 12-ounce bottles
Weighs 87 pounds when full
12-13″ high with a 16″ diameter

1/6 Keg
Holds 5 gallons – approximately 54 12-ounce bottles
Weighs 55 pounds when full
24″ high with an 11″ diameter

The Basics of Keg Pressure

Pressure is an imperative component of all fully-functional draft beer systems. It’s what keeps your beer carbonated and tasting fresh all the way from keg to glass. Having too much or too little pressure will affect the way your beer is dispensed, and you won’t be able to enjoy its full potential. These keg pressure pointers will help you find that perfect medium.

About Head Space

As CO2 enters a keg, it displaces your beer at a constant pressure. When you open the tap/faucet, beer flows out of the keg and into your glass due to a push from the CO2. The gas then fills the space where the beer was formerly housed, and that’s the “head space.” The CO2 fills the head space and maintains the pressure inside of the keg at the PSI set on your regulator [link]. This constant PSI keeps the beer carbonated by preventing CO2 leakage.

Keep it Straight

Your CO2 tank must be stored upright or it won’t work properly. Storing the tank improperly can also cause expensive damage to your regulator.

Find the Magic Number

Most ales and lagers produced in the US should be dispensed at 10 – 12 PSI. Stout and other nitrogen-reliant keg beers are usually dispensed at 25 – 30 PSI.

For the specific dispensing pressure for a particular keg, check with your local distributor.

Too Much Pressure

Too much pressure will leave you with foamy beer that comes quickly out of the faucet. If your beer is over-carbonated, the foam will appear tight with large bubbles.

If you encounter this problem, it’s easy to fix. Adjust your regulator pressure to the proper lower level and draw a few foamy pitchers. You can also use your coupler’s relief valve to bleed out the extra pressure. These measures will force your system to balance itself out again.

If the pressure is left too high for too long, CO2 will be forced into the beer resulting in permanently over-carbonated and excessively foamy beer. Thus, it’s important that you address this problem as soon as the issue is identified.

Too Little Pressure

Too little pressure will also force foam because the CO2 can break free from the beer as it enters your glass. If the pressure is not raised to the appropriate level, your beer will eventually become flat.

When you see foam or bubbles visibly rising in your beer hose, this is a telltale sign of low pressure. If your beer is under-carbonated, the foam will look loose, often described as appearing “soapy” with small bubbles.

To correct this problem, you should first make sure that your CO2 tank is properly turned on with gas remaining inside. Then, check to see the level at which your regulator is set. If your tank is functioning properly, you’ll know that your regulator is set to the right number and there are no obstructions in the air line. If this is the case, you may need to replace your regulator or gauge. Regulators do wear down with time and use, so you should generally replace them every 4-6 years.

Keg Tips, Tricks, and Rules to Remember

Keep it Calm

After any sort of transport or travel, give your keg some time to settle down. If you don’t, you’re likely to experience excessive foaming at tapping time. Remember that the beer inside of a keg is carbonated, so moving or shaking it will cause it to foam – just like a can of beer or soda. We recommend that you let your keg sit for an hour or so after transport.

Keep it Cold

Keg beer is unpasteurized, so it has to stay cold to stay good. As a general rule, think of keg beer as you think of milk: it needs to be refrigerated at all times. Keep your kegs between 34 – 40 degrees Fahrenheit and your beer will remain fresh and delicious.

Keep it Fresh

The beer inside a keg will retain its full flavor about 30 – 45 days after tapping. It’s difficult to pinpoint an exact amount of time, as a keg’s “shelf-life” is dependent on storage conditions and the brand/style of the beer. Generally, hoppy beers and those with a higher alcohol content will last longer because the hops and alcohol act as preservatives, inhibiting the growth of bacteria.

Keep it Clean

When beer does go bad quickly, it’s almost always one (or both) of two culprits: oxygen and/or bacteria.  Unfortunately, bacteria will eventually spoil unpasteurized keg beer – even when the keg is kept in the perfect storage conditions.

Modern scientists have discovered that the only way to beat the bacteria is to drink all of the beer in your keg, before the bacteria has a chance to ruin it – usually in that 30 – 45 day range.  Should you require critical consumption assistance, KegWorks research has found that good friends are usually willing to help.

The other culprit, oxygen, is particularly harmful to kegs tapped with a hand pump. A hand pump forces air (containing oxygen) into the keg, which in turn, forces the beer out. This is good. However, as soon as the oxygen is introduced in the keg, it causes the chemical reaction called oxidation.

Oxidation will cause the beer inside of a keg to go flat and acquire a sort of sour taste. Thus, a keg tapped with a hand pump should be consumed within 24 hours. Thankfully, neither of these processes render beer harmful to humans, but they do make it undrinkable.


  • Steve May 11, 2015 @ 5:22pm

    when i first tap a keg (always a craft brew IPA) it tastes great as intended for about 5 days or so. After that, its still okay, but not great like it was in week 1. After the second week, another drop off in taste. Still drinkable, but a far cry from two weeks ago. Am i doing something wrong with my CO2 pressure or is this just the nature of the beast? I use 5 gallon kegs in a refridgerator conversion kegerator. temp 37F, pressure 10-12psi. No foaming issues, great pours every time. (seven foot beer lines took care of the foaming). At 10-11 psi i get bubbles developing above the coupler (suggesting low pressure?) if i raise the pressure just to the point that those bubbles dont form (12-13psi), the beer loses flavor almost instantly (over carbonation?) What am i doing wrong?

    • Tony October 4, 2015 @ 7:22am


      Lots of things could be at play, but here’s my best theory:

      Modern IPAs are in some ways the most delicate beers in the world, as a huge chunk of their flavor is from delicate aromatics, which can cook off. Just for the sake for experimentation, dump (or set aside) two pints before you pour a pint to smell and taste. If that third pint tastes right, then you know the problem: all the beer you were drinking was that which was sitting (and aging) in the line. For one person’s kegerator, you generally want to stick with the shortest, thinnest line possible. If your beer line is bigger than 3/16″ ID, there’s half your problem right there.

      Like I said, my best guess. Good luck

  • John July 3, 2015 @ 6:52pm

    Every time I buy a new keg and hook it up I get all foam, the term true is in the low forties, my pressure gage is on about 10psi, still get foam , I i adjust the pressure up or even lower than 10psi , nothing seems to help,, I’m hoping you will have a solution.

    • Caleb Houseknecht July 6, 2015 @ 11:19am

      Hey John,

      Thanks for reaching out. First of all, I’d suggest lowering the temperature even more. 40 should be the highest, but you generally want to be in the 34-40 degree (Farenheit) range. Secondly, what kind of beer are you pouring? Ales and Lagers are good at 10-12 PSI, but Stouts and other nitrogen-reliant beers are best at 25-30.

      Lastly, are you seeing loose foam or small bubbles visibly rising in your beer lines? If so, the pressure is probably too low. Since you’re dispensing at 10 PSI, I can’t imagine it’s too high.

      Let me know about the kind of beer you’re pouring, take a look at possibly upping the PSI, depending on the beer, and try to hit that 34-40 degree sweet spot with your temperature. If that doesn’t work, we’ll re-assess. You can also always give us a call with questions at 877-636-3673.

      Thanks, John!

  • Shaun August 12, 2015 @ 1:41am

    I have a converted Guinness system that has worked great for 1 1/2 years. It was last tapped approximately a month ago. Worked great for two weeks. I then went on vacation for two weeks and it went untouched. Upon returning, it poured a half a glass and then went straight to foam. Every glass thereafter has been all foam. PSI remains at 28. Lines look fine. Nothing had changed. As I was at a total loss as to what was wrong, I replaced with a standard faucet just to see how it poured. It poured very fast since it was not a Guinness faucet but flowed black and immediately turned to foam in the glass. Could someone shed some light on what may be wrong? We are approaching football season and I desperately want Guinness flowing again.


    • Caleb Houseknecht August 12, 2015 @ 10:17am

      Hey there Shaun,

      That stinks, and we definitely understand the desire for fresh Guinness during football games. Why don’t you give us a call at 877.636.3673, and we can talk this through with you. Just describe the issue you’re having, and one of our Customer Care members will gladly walk you through some troubleshooting advice.

    • Hugo August 19, 2015 @ 9:03pm

      The 28 is too high, for too long. 28 psi in a busy place is ok, becasue there is no time for the beer to get over carbonated. Short draw 10 – 12psi , long draw 15 – 22psi that ‘s it. What you can do is shake your keg and then prime the pressure inside your keg until you get ridden of the over carbonation just make sure you don t do it too much you may get flat beer. Works like a soda can. Also the Guinness foam is created by the faucet so you don t need 28. Good luck

      • jeff October 23, 2015 @ 3:13pm

        Actually your pressure is fine for this one (maybe even a tad low). Your problem sounds like it is your gas blend. Guiness is a special beer called a nitro stout, it has a very low content of CO2 in it (typically 1.1 volumes by volume (similar to wine) whereas craft beers are 2.5 and domestics usually are 2.7). You want to push guiness with a 25% CO2 gas blend and a 75% nitrogen blend at a high pressure with a restrictor faucet. At this high pressure you can actually get a little bit of nitrogen absorption into your guiness. The end product is a good flow rate at your tap with the restrictor setup and a cascading effect as the nitrogen rises out of the beer quickly and pushes the co2 down. If you are using 100% co2 you are putting way way too much co2 under a high pressure into your guiness keg and you are going to overcarbonate your guiness and foam like a son of a gun. Change your gas blend and voila, problem solved. Nitrogen is actually used in other long draw set ups (higher pressure) to counteract the foaming in normal ales and lagers as well. Typically these setups will only require 40% nitrogen to counteract the CO2 absorption as you don’t need to displace as much CO2 because of the higher levels of CO2 that are already present in the beer. Now all of this can change depending on your temperatures….remember chemistry 101 where they told you that the soluability of gases rises in liquids as temperature decreases??? Temperatures, pressures, gas blends, and volume by volume, welcome to beer science.

  • Jane August 21, 2015 @ 4:26pm

    Our Keg tap was working one day and next it won’t move at all. Like it is frozen in place? Any suggestions?

    • jeff October 23, 2015 @ 3:25pm

      check the temperature of your freezer, maybe it is actually frozen in place?? :)

  • Steve August 23, 2015 @ 5:55pm

    I am kegging my home-brew for the first time. I keep my co2 regulator at 12 psi and lower it a little bit when I’m ready to dispense. While dispensing (I am using a picnic tap at the moment), I notice the co2 level going down. If my regulator is on, should it automatically take the keg pressure back to 10-12 psi? This has not been the case. I am manually turning the knob on my taprite regulator to put it back to these levels. Is there a way to maintain the levels w/o turning the knob every few drafts or is this normal and OK?

    • Jeff October 23, 2015 @ 3:23pm

      don’t lower it when you are ready to dispense, as the head space increases in your keg you want that CO2 going back into your headspace to keep your beers carbonated and from the CO2 breaking out of solution. Why were you lowering your CO2 pressure when you went to dispense in the first place? Was it coming out too fast? You want a flow rate of 2 ounces per 1 second so the co2 won’t break out of solution by slamming into the glass, time it yourself (7 seconds for a 16 ounce pint as the last two ounces should be a nice head at the top of the glass, doesn’t have to be dead on but you want to be somewhat close). If its coming out too fast you can always add a little restriction by lengthening your line, but don’t adjust your pressure down when dispensing it will only hurt your beer, and really doesn’t serve a purpose cheers!

  • Stephen Stenberg September 17, 2015 @ 12:33pm

    Opening new business with 29 taps. 27 Co2 and 2 nitos. Gas guys and beer guys dont know what amount of beverage grade CO2 and Nitro to order. Help! Steve

    • Caleb Houseknecht September 17, 2015 @ 2:33pm

      Hey Stephen,

      I gave your email to one of our Draft Beer Account Executives, and he’s going to be in touch with you. In the meantime, you can also feel free to shoot us an email at beer@kegworks.com, or give our Draft Beer guys a call at 866.881.BEER (2337).

  • Sarah October 19, 2015 @ 11:12am

    I have a 3 tap system kegerator. Co2 tank is inside the kegerator. It pours fine with 3 sixtels but when I have a 1/2 keg and 2 1/6’s after about 80-90 pours from the 1/2 keg all 3 taps pour at a dribble adjusting psi (regardless of up or down)allows the 1/6’s to pour but the 1/2 pours all foam. This only seems to happen when I have 1/2 keg combined with 2 1/6’s. No one can correct! Is it due to the uneven kegs and psi requirements? Please advise thank you

    • jeff October 23, 2015 @ 3:16pm

      What is your pressure at? how long is the 1/2 barrel lasting compared to the 1/6 barrels? What kind of beers are you pushing in each, craft, domestics, etc? Are you using one regulator, or are you using a step down regulator at each keg (think one reg per keg)? Let me know…

  • Dean November 21, 2015 @ 2:53pm

    Recently bought a used kegerator. Set up with 5 pound CO2, and all was great. But the CO2 only lasted one week! I checked for leaks but can’t seem to find any. Any suggestions? Thanks.

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