Several FOBs lines up with a closeup of FOB on the bottom

What's A Foam-On-Beer Detector (FOB) & Why You Should Care

Several FOBs lines up with a closeup of FOB on the bottom

When a bar is packed, bartenders will be busy making cocktails or dispensing beer into countless beer pitchers or beer glasses. One of the annoying things that could disrupt the service is when the draft beer runs out, and you get beer foam all over the place.

You don't have to experience these disruptions and wastage anymore when you have an FOB system! This device provides efficiency and cleanliness whenever a draft system runs out. It saves you money and prevents you from serving nothing but foam to your customers.

What is a Beer FOB System?

Stainless Steel FOB Detector
FOB System - Image by Perlick Corporation

FOB or "Foam On Beer" detectors are an innovative way to keep tabs on your draft beer! This device is beneficial if you have a long draw beer system. It is also called a beer saver or foam detector because they prevent pints of beer from being wasted.

The first FOB detection system was invented in the Ireland and the UK in the 70s. From this time, breweries have taken over ever since. They were created due to pressure put forth by bar owners who didn't want to waste beer every time a keg gets switched out.

In response to this demand, brewers teamed up with suppliers in designing finely crafted equipment that would help solve their problems.

An FOB system helps maintain the pressure in your beer lines to avoid losing as much beer, which happens when changing kegs. In other words, it detects when a barrel has run empty to which it responds by stopping the beer flow before it gets dispensed.

This way, the beer line remains filled with beer and void of air and gas. Normally, when you don't have an FOB installed, you need to detach the beer lines, purge the air, refill lines, and do other necessary things. The FOB system basically saves you the time and effort to do all this work.

How Does it Work?

Person pouring beer from a tab

Foam-on-beer detectors are the money-savers of every bar. The FOB Detector is installed in a pressurized dispense system, ideally where the keg is located at a distance over 5 meters away from the dispense faucet.

When you install a foam-on-beer detector on your beer lines, it becomes responsible for stopping the beer flow every time you empty your keg. This way, the foam won't build up, and the beer lines stay full. 

An FOB system features a chamber with a float inside that looks like a ping pong ball. The draft from the keg is what makes the float inside the FOB go up. When this happens, the beer flows into the tap. 

When the keg is cleared of beer, the FOB detects it, and the float drops immediately, blocking the passageway of the beer. At this point, the chamber will only be filled halfway with beer, but the beer lines remain full. 

When you have tapped a new beer keg, the beer flow will go back as the float goes up again and opens the passageway. 

How Much is Wasted if There’s No FOB?

The wasted beer from one keg without an FOB can amount up to 64 ounces. The amount of beer loss is dependent on the length of the line and the number of barrels you use at a particular time.

Here is a guide to help you determine the worth of beers wasted when you don’t have an FOB installed.

Length of line

40 kegs per month 

60 kegs per month

80 kegs per month

25 feet




50 feet




100 feet 




These amounts are only estimates as the price of beer varies on the type, style or brand. 

How to Use an FOB Detector?

Using an FOB system is pretty easy. Follow these steps correctly so you can make the best out of this device and prevent any malfunction.

Watch Out for the Flow of Beer

  1. Observe the flow of your beer when dispensed from the tower. It should be at a steady pace and has a slightly angled direction.
  2. When you notice that the flow becomes weak or there's no more beer coming out, close the faucet immediately. At this point, the float should have dropped and covered the passageway already.

Tap a New Keg

  1. If you have multiple kegs, identify first which one needs to be changed.
  2. Pull the empty keg offline by removing the connector.
  3. Get the new keg and sanitize its valve and the coupler of the connector. Afterward, tap the new keg and drop the handle to start the flow.

Resetting the FOB

  1. Go back to the FOB and identify the vent mechanism.
  2. Vent the FOB by covering it with your index finger. Doing this releases the foam and gas from the chamber and allows the beer to flow up from the keg back to the FOB.

Reposition the Float

  1. Although the chamber has already been filled with beer again, the float is still down at this point. To bring it back up, dislodge the float by turning the lever counterclockwise until it points at the red mark.
  2. When you see the float up again, turn the lever again (counterclockwise), so it will return to the green mark.

FOB System FAQ

1. Why does beer create foam?

Gas bubbles are a natural occurrence in beer, and they are seen as soon as you open your bottle. Scientists have named it "nucleation."

The bubbles of gas trapped inside the beer are responsible for creating the beer's head of foam and are caused by gases released during fermentation, bottling, and kegging because of pressure and condensation. The foam is composed of protein, yeast, and residues of hops.

The foam gives the beer a creamy and full-feeling mouthfeel that's often noticed in hefeweizens, farmhouse ales, and other wheat beers. Those made with oats or rye also make excellent foam heads for different reasons depending on their style preference.

There are a number of factors that affect the production of beer foam. These include how the beer was brewed, its ingredients, the kind of glass you'll use to serve the beer, the level of carbonation, and the manner of pouring the drink.

Foam disappears faster when they come in contact with any residual oils, whether in the beer glass or on your lips.

2. What are the benefits of an FOB system?

Beer FOBs are a must-have for any barkeep who wants to keep their lines filled with beer from start to finish. You will never have to refill your long draw beer line and purge air from the beer system with an FOB. It also ensures that your customers will drink mostly beer and less foam. 

Installing an FOB means more efficient production, less wasted foam, and your customers will not experience inconveniences. Furthermore, it will save you from additional labor costs from having someone clean the mess of blown-up kegs.

Also, the FOB-detecting system will save you time and money by eliminating most of the foaming that occurs when switching kegs in your long draw system. You can lose up to 64 ounces of beer when you change the empty keg!

3. When must a FOB detector be reset?

A beer FOB system detector should be reset every time you tap a new keg.

4. How do I clean and maintain an FOB system?

FOB detectors should be maintained and cleaned regularly to keep them functioning optimally. We recommend that you disassemble your FOB detector for maintenance every three months using a beer line cleaner.

Even though a beer line cleaner is excellent at removing all of the organic waste buildups in your FOB, it isn't very effective for removing minerals. For a flawless cleaning process, an acid beer line cleaner is a must-have.

Not only can it remove all of the pesky brewing residues, but it also helps to break down unwanted minerals and stones in your lines! It's essential to keep your FOB clean at all times as it also plays a role in the beer's taste.


In a bar setting, it's crucial to prevent any wastes so you can increase profits. One way to help you achieve this goal is by investing in an FOB detector!

With the money it saves you every month, not only will it cover its cost but also lets you earn more for years to come!



  • Need foam detector


    Krishna Singh Negi

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