Draught Beer Made Simple:
It’s all about Temperature, and THEN Pressure
Picture a brewpub where you’ve been served a pint of draught beer with the perfect amount of foamy head. Now picture that same brewpub and imagine lots of foam. The bartender pouring, tipping, dumping out foam, then pouring some more. Or pouring and setting the beer aside to let the foam settle. And then you’re finally served a beer after the bartender wipes off the exterior of the glass. Same place. Two completely different draught beer experiences. Why?
Number 1 cause is temperature. Number 2 cause is temperature. Number 3 … temperature. Number 4 … temperature. And, finally, the Number 5 cause of excess foaming is Pressure. And this is in order of importance. This is sequential: 1 to 5. Seriously… Save Pressure for last.
Let’s review the 4 Causes from Temperature…
- Cause #1 “The Temperature of the Beer In the Keg”… IF the temperature of the beer in the keg is 50°F, and you are dispensing using a commercial keg box (Direct Draw), walk-in cooler (Long Draw), or kegerator (typically home dispense), you are not pouring that beer for approximately 24 hours. Why? The Delta T OR the difference in temperature between the Keg Temperature and the Refrigeration Temperature [50°F – 38°F = 12°F] is relatively small. Initial cooling to 45°F will take approximately 6-8 hours. At 45°F draught beer is difficult to dispense without excessive foaming.
- Side Conversation: If the temperature of the refrigeration source was -109°F you would be pouring 38°F beer in 75-90 minutes. A controlled acceleration of cooling is an interesting concept.
- Cause #2 “The Temperature of the Refrigeration Unit” – commercial keg box, walk-in cooler, or kegerator. If the Beer in the Keg is 38°F and the refrigeration temperature is 50°F that keg will warm to 45°F in 2-3 hours, and at that temperature it’s challenge to dispense beer without excessive foaming.
- Important Information / Profitability: 25% of foam is beer. It’s true. Pour a glass of foam and let it settle. You will end up with a glass of beer that is one-quarter full. The Germans call this a Schnitt (cut or split). The bartender intentionally pours less than one quarter beer and then more than three-quarters of foam, 6 minutes or so later the glass is half full of beer and the customer is charged for half a glass
- Cause #3 “The Temperature from Outside the Refrigeration Unit to the Shank & Faucet (this includes the beer tower).” If the beer in the keg is 38°F, and the refrigeration unit is 38°F, but the sun is shining on the beer tower and faucet heating it to 72°F, then the beer will foam. The first beer will foam a lot. The second beer will foam less. The third beer will pour perfectly. Why? You have used your nice cold beer as a liquid refrigerant to cool from the refrigeration unit, through the tower to the shank & faucet. Wait another 10-15 minutes between beer pours and you will pour another 3 beers to get 1. And, remember, 25% of foam is beer. Think Profitability.
- Cause #4 “The Temperature of the Glassware.” If the beer in the keg is 38°F, the refrigeration unit is 38°F, the tower to the faucet is 38°F, and the glass is room temperature, you will pour foam. Carbonation (CO2) does not want to be in a liquid. It wants out. An over-carbonated soft drink, for example, will tickle your nose with escaping CO2. Warm glassware helps the CO2 escape while freshly rinsed relatively cold glassware makes it that much harder for the CO2 to leave. The faster the CO2 degases the flatter (less carbonated) the beer becomes.
- Side Conversation: Frozen glassware is a different animal altogether. IF DONE RIGHT it can be a nice experience. The problem is that it’s difficult to do it right, and typically, you end up drinking beer mixed with glass sanitizer solution. The reason for this is simple. In a commercial account, glasses are washed with a sanitizer solution. For the sanitizer to work properly it must air dry completely after it is washed (evaporating the sanitizer into the atmosphere). If newly washed glassware is put directly into a freezer, the sanitizer does not have time to work as designed and is left on the surface of the glass and then frozen in place. Add beer and the sanitizer will move from the frozen inside wall of the glass into the beer. Nice, right?
And finally, that leaves Cause #5 Pressure.
Divide Pressure into thirds: too much pressure on the beer, too little pressure on the beer, or the biggest pressure problem: no pressure on the beer (the CO2 source is empty, or the CO2 source is shut off). No gas = big problems.
Let’s start with ‘No Pressure’…
Imagine we have 3 kegs on tap in a commercial keg box. One is almost full, one is half full, and one is a quarter full. The CO2 runs out. No gas = big problems. No one notices that the gas has run out and the bar keeps serving beer.
- The keg that is full will start foaming after a few beers because there is little head space in the keg which means there isn’t very much CO2 in the head space (push pressure). CO2 wants out of liquid. The CO2 in the beer will leach out of the beer and begin to fill up the head space and provide the push pressure needed to dispense beer. The more beer that is dispensed from this almost full keg, the more headspace is created. The more headspace that is created in turn creates more space for CO2 to leach out of the beer and into the additional head space. You’re basically degassing the keg and making the beer flat.
- The Keg that is half full will continue to pour. CO2 will leave the beer for the head space, but because there is already CO2 in the headspace at a pressure slightly greater than the CO2 in the beer [carbonation value of the beer plus push pressure], foaming issues will be minimal. Simply put, we’ve got some spare CO2 in the headspace that we can use to push the beer for a little while.
- The keg that is a quarter full will dispense with minimal foaming issues at the end. This is because three-quarters of the keg is full of CO2 at carbonation value plus push pressure. To further simplify this point, we have a lot of spare CO2 in the headspace. This beer will not pour as well as it would if it remained under carbonation (we are slowly degassing the beer), but it will pour.
Now, imagine that the commercial keg box somehow is set up with old-timey secondary pressure regulators on each line, which is technology the beer industry borrowed from the welding industry over 100 years ago (that hasn’t changed much since). Then imagine the CO2 source is empty or has been accidently turned off. A well-intentioned bartender or wait staff person, who may know enough to be dangerous, will see that the freshly tapped keg is not pouring well, but the other two kegs are pouring nicely. That person MAY do one of two things to correct the ‘pouring issue’ from the almost full keg: turn the pressure up or turn the pressure down… Up or down is the only adjustment that person can make. Those seem to be the two choices. But remember, this isn’t a pressure-on-beer issue. It’s a lack of dispense pressure, a lack of CO2, a “no gas = big problems” thing. The right decision is to change the CO2 bottle OR turn the shut off valve back on. The right solution does not require a pressure change up or down. IF well-intentioned staff turn the pressure up or down and later it’s discovered that the CO2 cylinder needed to be changed, then dispense pressure will have been changed from a ‘good technical setting’ to a ‘well-intended but bad setting.’
Now let’s finally deal with too much or two little pressure on the beer. This is the issue that seemingly can be fixed with a pressure adjustment.
Let’s go back to the three kegs example again: one keg is almost full, one is half-full, and one is a quarter full. And let’s assume that we have plenty of CO2 to keep the carbonation in the beer and add just enough push pressure to dispense the beer. And we’re having foaming issues: do we turn the pressure up or do we turn the pressure down? Down is most likely wrong. And here’s why. If we are having foaming issues with a new keg, and the other two kegs are pouring fine, chances are the beer is warm. Take a temperature by pouring a three-quarters full glass of beer. Dump it out of the glass. Pour a second glass three-quarters full, stick a probe thermometer down past the foam and into the beer. A temperature of 45°F or higher points to a temperature issue, not a pressure issue, and that you should not be pouring that beer for another 24 hours. And you should not be adjusting pressure…
But what if you DO adjust pressure?
- Turn the Pressure Down → Why turn the pressure down? Because it looks like beer is flying out of the faucet and into the glass. The glass is filling up quickly, really quickly. If you could slow down the flow, maybe the beer wouldn’t be so foamy? Unfortunately, this doesn’t reflect what is actually happening. Remember CO2 not wanting to stay in beer? The warmer the beer the more CO2 can escape? What you’re seeing is CO2 escaping, and in the rush to escape the CO2 is creating foam. Turning the pressure down is simply allowing the CO2 to escape faster, which means more CO2 is escaping.
- Turn the Pressure Up → Let’s say you have bar staff who know a thing or two about a thing or two. And they realize that the way to pour 45°F beer is to put more pressure on the beer to help keep the CO2 in solution. That’s right, that will work. They turn the pressure up, and they manage to serve beer by either pouring 1 ½ beers to get 1 beer, or 2 beers to get one beer, or worse. End of night everyone goes home. Meanwhile the commercial keg box is doing its job. It’s cooling the keg. As the keg cools, the beer is able to absorb more CO2 from the headspace into the beer. The colder the beer gets the more CO2 it absorbs. A few days later the bartender has force-carbonated the beer to higher than the brewer intended. And the result is that the last quarter of the keg will pour like a milkshake.
Side Conversation: Profitability is time & money. The time it has taken staff to pour and sell warm draught beer is greater than the time spent pouring trouble-free beer. The foam that was dumped in order to serve a proper pint created further time delays and cost the bar money (foam = money; remember 25% of foam is beer).
Why would you want to install old-timey secondary pressure regulators on each line and risk changing draught beer dispense pressures from the settings determined by the professional installer or equipment maintenance person? Why give people the chance to change set pressures from right to wrong?
The Gov Reg™ (www.govreg.us) is designed to replace old-timey secondary regulators (see page 17 of Draught Beer Quality Manual, 4th edition). The Gov Reg™ is an inline secondary pressure regulator that is set using an adjuster tool by the installer, draught beer dispense maintenance company, or properly trained personnel who may work for the establishment (or be contracted by the establishment). OR the draught beer suppliers’ technical staff. OR your draught beer line cleaner, who oftentimes are part of the draught beer equipment installation company.
Finally, back to Temperature, Temperature, Temperature, Temperature and Pressure… By using the Gov Reg™ on every beer line and setting each to the proper dispense pressure, you have locked down a key variable in draught beer dispense. If you have a keg that begins to foam, check to see if you still have CO2. IF the keg has just been tapped, and everything else is pouring well, and you have CO2, do not pour that beer. Wait 24 hours.
For everything else… IF all of the beers in the system are foaming, it’s a temperature issue. Start troubleshooting by taking beer temperatures. Then figure out why your temperatures are high. It may be a refrigeration issue (service or replacement); it may be a keg handling issue (require that all kegs sit in the walk-in for 48 hours before tapping); it may be a tower issue (call in your installation company to repair or replace your tower or glycol deck).
IF you address temperature issue(s) and lock down pressure (with the Gov Reg™), you will pour draught beer without foam. IF you keep your beer lines and glasses ‘beer-clean’, the draught beer you serve will taste better than the same beer bottled or canned. And if you do these things well, keep it up because you’ve created a money-making machine. There are bars in the US that make so much money on draught beer that it pays the rent, employee salaries, cost of beer, cost of food, cost of liquor. Which means that all the money brought in on food and liquor is profit. That’s how much money a bar can make on draught beer dispense.
A manager at a Hard Rock in South Lake Tahoe shared with me that when she was managing a Chevys Fresh Mex Restaurant, she knew she would make her numbers every month if she paid attention to draught beer dispense. And she could estimate her yearly bonus on draught beer sales.