[James K]

I made a sour from bottle dregs back in December. The beer has since been bottled and at first had noticeable THP flavor. It has since reduced and I can no longer identify it as well as I could 3 months ago.
I have shared some of this brew and people have told me it also has a vinegar quality. When I read the BJCPStyles guide for mixed fermentation sours it says “Acidity should be firm yet enjoyable, but should not be biting or vinegary; prominent or objectionable/offensive acetic acid is a fault.”

Is vinegary considered off flavor or fault? Where does it come from in the brewinger, fermentation, or bottling process? And does it go away over time? I heard it won’t and could get worse depending on oxygen levels. The beer was bottle conditioned.

Thank you for comments and feedback.

[dmtaylor]

Vinegar will not improve and will only get worse.  It comes from acetobacteria that are present in the air, and is caused by exposure of the finished beer to air.  This bacteria actually uses oxygen to turn alcohol into vinegar, so while vinegar increases, the ABV will decrease.  You can often but not always detect acetobacter by the tell-tale rubbery pancake-like "mother" that floats on the surface.  If you don't see a mother right now, you might later.

Avoid prolonged exposure to air-space in your fermenters to avoid this in future.  This batch might be lost.  However, it might actually make some mighty tasty salad dressing!

[James K]

Vinegar will not improve and will only get worse.  It comes from acetobacteria that are present in the air, and is caused by exposure of the finished beer to air.  This bacteria actually uses oxygen to turn alcohol into vinegar, so while vinegar increases, the ABV will decrease.  You can often but not always detect acetobacter by the tell-tale rubbery pancake-like "mother" that floats on the surface.  If you don't see a mother right now, you might later.

Avoid prolonged exposure to air-space in your fermenters to avoid this in future.  This batch might be lost.  However, it might actually make some mighty tasty salad dressing!

I wouldn’t say it’s strong. Just noticeable.
I never saw a rubbery pancake-like “mother” but the beer did form a pellicle during fermentation and I think in the bottle conditioning process as well. I also don’t think it had a lot of airspace in the five gallon carboy but I did stir this batch while bottling using priming sugar ( trying to get more consistency for carbonation) (I’ve since switched to drops).

All in all I don’t think the batch is lost (yet). But I haven’t been drinking it either, because I wanted the THP to go away.