Foaming at fill on a Meheen
Foaming is either the beer or the fill sequence, and one test tells them apart. Fill a bottle very slowly with the speed valve a quarter turn open, from the same tank, at the same temperature. If it foams anyway, the problem is upstream of the machine.
Work through it in this order
Cheap and common first, expensive last. The order is the information.
-
Do the slow-fill test first
Same tank, same temperature, very slowly, very slowly.
-
If it foams even at an artificially slow fill, look upstream
Temperature. Colder product holds CO2 in solution. A cellar or chiller that’s drifted a couple of degrees shows up at the filler first.
Carbonation. Over-carbonated product foams however good the machine is.
Pressure drop upstream. Anything that drops pressure sharply between tank and filler breaks CO2 out of solution before the beer arrives. A partly closed valve, a restriction, a long or badly routed line.
Dissolved air. Oxygen picked up upstream makes foaming worse, and it’s worth chasing for shelf-life reasons anyway.
-
If it fills calmly: the sequence
Counter-pressure filling works by pressurising the bottle before the beer enters, so the beer never sees a pressure drop. When the sequence is off, foam is the first symptom.
- Pre-evacuation and purge. Is the bottle properly purged first?
- Counter-pressure hold. Is it reaching and holding pressure before the fill starts? A bottle that isn’t sealing can’t hold it.
- Snift and vent. Venting too fast drops pressure suddenly and foams the bottle at the last moment. If your foam appears after the fill rather than during it, look here first.
- Fill speed, too fast for the carbonation.
-
Leaks, which are more common than people expect
A Meheen that won’t hold its sequence is very often leaking somewhere in the lines rather than suffering anything dramatic. Pressurise it, leave it, come back and see where it’s gone. It’s a cheap test and it finds a lot of these.
-
Valve and seal condition
A head that doesn’t seal on the bottle can’t establish counter-pressure, and behaves exactly like a sequence fault. One head bad and the rest fine is a sealing problem in almost every case.
-
Air supply, underneath all of it
A Meheen wants roughly 15 cfm at 90 psi (25 m³/h at 6.2 bar), dry and clean, through a dryer and a coalescing filter. Marginal air gives sluggish valve action, which gives an inconsistent sequence, which gives foam. Check the coalescing filter and the dryer.
-
Bottle variation
Different glass, different neck geometry, poorer seal, less reliable counter-pressure. If the foaming started when the bottle supplier or the batch changed, that’s your first suspect and it isn’t a machine fault.
Four things get us to a diagnosis in one reply most of the time: does it still foam at a slow fill, is it all heads or some, does the foam appear during the fill or at snift, and what changed recently. Free, within 24 hours.
Ten seconds of video of one bottle filling tells us more than a page of description.
Then it’s worth sending it to us
How it behaves at a slow fill, all heads or some, during the fill or at snift, and what changed. Free, within 24 hours.
If you’ve isolated it to specific heads, send a photo and we’ll identify the parts.
The questions this one raises
Is foaming a machine fault or a beer fault?
Both are common. The slow-fill test separates them in ten minutes.
The foam appears at the end of the fill, not during it.
Look at snift and vent. Venting too quickly drops pressure suddenly.
One head foams, five are fine.
Sealing problem on that head, nearly always.
Could my air supply cause foaming?
Indirectly, yes. Marginal air makes valve action inconsistent, which makes the sequence inconsistent.
Can you diagnose this remotely?
Often. Ten seconds of video of one bottle filling tells us more than a page of description.
Tell us what your machine’s doing
A photo, a line about what the machine’s doing, and the serial number if you can find it. Free diagnosis. Answer within 24 hours.