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What are Foam On Beer Detectors? (FOBs)

By Rich Pulsifer August 01, 2020

What are Foam On Beer Detectors? (FOBs)

Foam on Beer Detectors, FOBs for short, have also garnered the nicknames “beer savers” and “foam detectors”. These small yet effective devices have saved countless pints of beer, or foam, from being lost at the beer tap through draft beer systems around the world. If you haven’t got these on your draft system already, you should really be looking into it!

What Does a Foam on Beer Detector (FOB) Do?

A foam on beer detector fills with gas when the pressure drops inside it; filling the beer entry hole with a small buoy. This pressure drop comes because the keg it is connected to is empty. The FOB keeps the beer in the line pressurized, reducing the lost beer typically associated with changing kegs. This is especially beneficial in long draw systems where the loss of beer for each keg emptied without a FOB can head into tens of pints.

Do I need a FOB on my Draft System?

A FOB is going to optimize just about any draft system, however they really help reduce wastage and time spent changing and pulling through a new keg on long draw draft systems; those over 25ft. The longer the draft system the more beer you’re potentially losing without a FOB!

If you use beer pumps FOBs are a must! Pumps need liquid in them to run. Naturally a beer pump needs beer in it. Not using a FOB means you run the risk of emptying your beer pump and having it run dry. This is the most common cause of pump failure and that’s not something anyone want to happen. Get yourself a FOB  for each keg and sleep peacefully at night knowing that your pumps won’t run dry.

How Much Can a FOB Actually Save Me?

Beer lines vary but the standard beer line, 3/16” diameter, is the thinnest and contains approximately 1/6oz per foot. Therefore, every 6ft of beer line equates to at least 1oz of lost beer; the longer the line the higher this number gets. Most importantly not having a FOB means that when you empty a keg there’s going to be depressurized beer in the line which turns into foam, this needs at least an equal -and often more- amount of beer in order to push this foam through and re-pressurize the line. Without a FOB to stop this depressurization the amount of beer it takes to re-pressurize the beer in the line rises with the length of the line.

Servicing and Cleaning Beer FOBs

Being inline with the kegs FOBs get cleaned out every time your draft system gets cleaned (hopefully that’s at least every two weeks!). Whilst this is sufficient for cleaning, to ensure the longevity of your FOBs they should be disassembled, serviced, and cleaned every six months.


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