How a Commercial Draft Beer System Works.

A draft beer system looks simple from the customer side: pull the handle, beer comes out.

Behind the bar, there is a lot more happening.

A commercial draft beer system has to move beer from a refrigerated keg to the faucet while maintaining the right temperature, carbonation, pressure, and flow rate along the way. When those pieces work together, you get a consistent pour. When one is wrong, you can end up with foam, flat beer, slow pours, excessive waste, or a system that never seems to work quite right.

Here is what is actually happening between the keg and the glass.

It Starts With the Keg

A commercial beer keg is more than a stainless steel container full of beer.

Inside the keg is a tube called a spear that extends toward the bottom. When the keg is properly tapped, gas enters the keg while beer is pushed up through the spear and out into the draft system.

That distinction matters because a draft system is not simply letting beer fall out of a keg. The system uses controlled gas pressure to move the beer while also maintaining the carbonation level the brewer intended.

The Keg Coupler Connects Beer and Gas

The keg coupler is the connection point between the keg and the rest of your draft system.

It attaches to the valve on top of the keg and creates two paths:

• Gas enters the keg.

• Beer leaves the keg.

Different keg valves require different couplers. The American Sankey D-system is common across U.S. breweries, while imported and specialty beers may use different coupler types.

This is why changing the beer lineup at a bar can occasionally involve more than ordering a different keg. The new product still has to be compatible with the equipment connected to it.

Gas Does More Than Push Beer

CO2, nitrogen, or a blend of the two provides the pressure used to dispense beer.

But pushing beer through the line is only part of the job.

For most beers, the gas system also needs to maintain the proper level of carbonation inside the keg. Applying the wrong gas or pressure can gradually change the beer itself.

Too much CO2 can increase carbonation. Too little can allow carbonation to leave the beer. Either problem can eventually show up at the faucet as poor pour quality.

This becomes particularly important in long-draw systems. Moving beer through a longer system may require more applied pressure to overcome resistance. Depending on the beer and system design, a properly selected CO2/nitrogen blend can allow that higher dispensing pressure without forcing too much CO2 into the beer.

Nitrogenated beers such as Guinness have their own requirements and should not simply be treated like a standard lager or ale.

There is no single pressure setting that is correct for every draft system.

The Regulator Controls the Working Pressure

Gas cylinders store gas at pressures far higher than what you would apply directly to a keg.

The regulator reduces that cylinder pressure to a controlled working pressure appropriate for the draft system.

Many commercial systems also use secondary regulators so individual products can be adjusted separately.

That matters when your draft list contains beers with different carbonation requirements. One universal pressure setting across an entire system may not be the right answer.

The correct pressure depends on several things, including the beer, temperature, elevation, line size, system resistance, and the distance the beer needs to travel.

The Beer Line Creates Resistance

Once beer leaves the coupler, it travels through beverage tubing toward the faucet.

The diameter, material, and length of that tubing matter.

Beer moving through a draft line encounters resistance. Elevation changes and system components can add resistance as well.

That resistance is intentional.

A properly designed system balances the pressure pushing the beer with the resistance working against it. The goal is controlled flow at the faucet while maintaining the beer's intended carbonation.

This is one reason adding random lengths of tubing or simply turning the pressure up when a system is pouring poorly can create more problems than it solves.

Draft systems need to be balanced as a complete system.

Short Systems and Long Systems Work Differently

The distance between the keg and faucet determines a lot about how a draft system needs to be designed.

Direct-Draw Systems

In a direct-draw system, the keg is stored very close to the faucet.

Think of a commercial kegerator or a faucet mounted through the wall of a walk-in cooler.

The beer only travels a short distance before reaching the glass.

These systems are relatively simple because the entire beer path can remain refrigerated without needing to transport beer through a long section of the building.

Remote and Long-Draw Systems

Things get more complicated when the walk-in cooler is in a basement, back room, or another part of the building.

Now the beer may need to travel dozens of feet before reaching the bar. Keeping it cold throughout that entire journey becomes critical.

Shorter remote systems can sometimes use refrigerated air to maintain line temperature.

Longer commercial systems generally use glycol cooling.

What Does Glycol Do?

A glycol-cooled draft system uses a separate refrigeration unit, commonly called a glycol power pack, to circulate a chilled glycol solution through coolant lines.

Those coolant lines travel alongside the beer lines inside an insulated bundle called the trunk line.

The glycol does not mix with the beer.

Instead, it removes heat from the trunk and helps keep the beer at a controlled temperature while it travels between the walk-in cooler and the faucet.

This is especially important in buildings where the beer has to travel through warm ceilings, mechanical spaces, kitchens, basements, or other areas outside refrigeration.

A glycol system also has to be sized correctly. The number of products, number of faucets, length and construction of the trunk line, ambient conditions, and system layout all contribute to the refrigeration load.

Simply installing a larger-looking glycol unit is not the same thing as properly sizing the system.

The Tower and Faucet Are the Final Stretch

At the bar, the beer travels through the tower and reaches the faucet.

By this point, most of the work responsible for a good pour has already happened.

The beer has been stored at temperature, supplied with the appropriate gas, pushed through a balanced beer line, and kept cold during transportation.

The faucet controls the final release into the glass.

A good faucet matters, but swapping faucets will not fix a badly balanced or poorly cooled draft system upstream.

A Good Draft System Is a Balanced System

There is no single component responsible for a perfect pour.

• Temperature affects carbonation.

• Gas pressure affects carbonation and flow.

• Beer-line diameter and length affect resistance.

• Elevation affects the pressure required to move beer.

• Cooling affects what happens to the beer between the keg and faucet.

All of those variables interact.

That is what technicians mean when they talk about balancing a draft system.

A system can have expensive equipment and still pour poorly if those components were not designed to work together.

On the other hand, a properly designed system should feel almost boring during normal operation. You tap the keg, open the faucet, and the beer pours consistently.

That simplicity at the bar is the result of getting everything behind the wall right.

Planning or Fixing a Commercial Draft System?

Draft Choice designs, installs, services, cleans, and troubleshoots commercial draft beverage systems throughout New York City and beyond.

Whether you're planning a new bar, moving a walk-in cooler, adding products, upgrading an older system, or dealing with a draft setup that has never poured correctly, the first step is understanding the entire system instead of treating each component separately.

A good draft system should be designed around your space, your beverage program, and how the system will actually be used every day.