Oxidisation in the keg

[JackoNZ]

Has anyone experienced a beer getting oxidised once in the keg? I kegged an Oktoberfest beer a few weeks ago, after 2 weeks in the keg I tried a glass and it tasted great, very malty and beer like. A week later I went to fill a few bottles and I filled a glass at the same time. I thought I got a hint of vinegar on the nose but wasn't sure, tested it on my girlfriend and she picked up the same. The taste is fine, although not as good as it was last week but that could be because of the aroma effecting it.

I'm presuming the beer has become oxidised and that is why I am picking up some vinegar aroma. But I'm stumped as to how that can happen once in the keg. I have had it hooked up to the gas all the time, nothing on the out connection until I came to taste. If there was a leak then surely I would have lost all my gas, so can't imagine it's that.

Any thoughts?

[jt]

I thought oxidised was cardboard - I've done that, I think - with a bit of slishy-splashy when kegging.
Is vinegar an infection, aceto-unspellable ?

*edit* - it's not with some repitched 34/70 is it - gulp - as i'm doing that right now

[JoKing]

I dont want to have to say it mate, but..........

Sounds to me like an acetobactar infection... most likely source: malt grain in the direct vacinity of where you pitched your yeast - or something to that effect. It could have even been transferred from the hose you used to transfer the wort from your mash tun into your kettle. They are tricky little bastards - I think they dont die until 80 degrees C. Think back around brew day and try to isolate where sweet wort or malt may have come into contact with cooled wort - this may be where you could have picked this up.

[Brendon]

As Jo says.
Acetobacter is an aerobic bacteria and quickly turns o2 to vinegar. Oxidation takes quite a bit longer.

Try caustic, followed by boiling water, followed by iodophor. It may just do the trick.

[jt]

most likely source: malt grain in the direct vacinity of where you pitched your yeast

that's the probable cause of what I suffered a few years ago - remember the jar of astringent wort I took round to Stu's one brew day ?

Probabale cause, milling in the garage with the ferementers

[JackoNZ]

Thanks guys, I will need to double check this as a friend tried a bottle yesterday and said he didn't pick up the vinegar. Haven't had chance to look into it yet but I'll try another bottle tonight and see if it's still there.

Is this acetobacter stuff bad for your health or is it just the vinegar aroma (and taste I guess eventually)?

jt - it wasn't re-pitched 34/70, so nothing to worry about there. I do keep all my grain in bags, in cardboard boxes in my brew cupboard where everything else goes so maybe that's a problem. I BIAB so no mash tun involved, really can't think of when sweet wort would have got in contact with cold wort, I'm pretty anal on the cleaning front. Would you expect acetobacter to take hold immediately though or after sometime? I ask because the beer tasted great when I first tried it, a week later, it's not the same.

[Reviled]

"Is this acetobacter stuff bad for your health or is it just the vinegar aroma (and taste I guess eventually)?"

Nah I dont think so mate, just the aroma and taste you need to worry about...

If it truely is acetobacter it would take a while to take hold, as in the beer would be fine at kegging and would start to sour with an infection in the keg... One question tho - Clarity? Was it reasonably clear on kegging and has it started to go slightly hazy at all?

[JackoNZ]

I'll double check tonight but maybe slightly hazy, not unusual for me though. Plenty of time in the fridge clears it up eventually.

And it sounds like it's difficult to get rid of this stuff too? Hopefully it's just in the keg, that's been soaking in Napisan since the weekend so I'll clean that up again tonight, chuck some boiling water through it too.

[jt]

Would you expect acetobacter to take hold immediately though or after sometime?

When I had a problem with it, it was evident in the fermeter from a few days in, but there again I was probably a bit shabby with my habits then.