When beer starts pouring foamy, the instinct is to blame the gas. Most of the time it is temperature. Beer that warms anywhere between the keg and the tap releases dissolved carbon dioxide, and that gas comes out as foam in the glass. Find where it is warming up and you have usually found the fault.
Why temperature causes foam
Carbon dioxide stays dissolved in cold beer and comes out of solution as it warms. A couple of degrees is enough to make the difference between a clean pour and a glass that is half head. That is why foam problems so often appear gradually rather than suddenly: the system is not broken, it is just no longer holding the temperature it used to.
The three places beer warms up
- The cellar or keg room: if the kegs themselves are warm, nothing downstream will save the pour. This is the first thing to check and the most commonly overlooked.
- The glycol system: the glycol bath should be holding close to freezing and circulating properly. A weak pump, low glycol level, an iced-over bath or a refrigeration fault all reduce how much cooling reaches the lines.
- The python and the last few metres: damaged insulation, a line run through a warm void, or a long uncooled section at the tower will all let beer pick up heat right at the end of its journey.
Why it gets worse exactly when you are busy
This is the pattern almost every venue describes, and it is diagnostic rather than coincidental. At a low pour rate, beer moves slowly and has plenty of contact time with the chilled lines, so even a system running below par delivers cold beer. Push the rate up on a Friday night and beer travels the same distance far faster, with less time to be cooled, while the cellar is warming from door traffic and the glycol system is working harder than it has all week.
The practical consequence: a beer system that behaves perfectly at 2pm on a Tuesday can still be genuinely faulty. If the problem only shows under load, that is when it needs to be looked at, and it is worth saying so when you book the visit.
What to check before calling
- Glycol bath level and temperature, and whether the pump is actually running
- Whether the cellar or keg room is holding its temperature, especially late in a busy shift
- Insulation on the python, particularly at joins and where it enters the bar
- Whether the problem affects every tap or only some, which separates a system fault from a line fault
- Whether anything changed recently: a keg moved, a new line run, a door left open
When it is not temperature
Gas pressure set incorrectly for the line run, a faulty regulator, dirty or worn line components and damaged couplers all cause foam too. They are worth ruling out, but they tend to produce a consistent problem rather than one that tracks with how busy you are. A fault that follows your trade curve is pointing at cooling.
Foam is expensive in a way that is easy to underestimate. Every glass poured away is product paid for and not sold, and it adds up quietly across a weekend well before anyone decides the problem is bad enough to call about.