Does vinegar production cause the airlock to bubble?

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zppz

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I started a kit beer and a kit cider at the same, at two weeks I racked them into buckets with a tap at the bottom. They tasted ok, cider was perhaps a bit sweeter than expected. Due to stupid lockdowns and postal system overload I didn't have the sugar drops on hand that I wanted, so I ended up waiting another ten days, and during that time my curiosity got the better of me. I used the tap to let out about a 1/4 glass of each, which made the airlock bubble backward just once.

Shortly after that, the cider started up bubbling again, slow (about one bubble per minute or two) but steady for what has now been four days. I took another sample and it seemed to have a veeeery slight vinegar taste, although it was also fairly fizzy so perhaps it was the carbonation. There was no temperature change and I didn't shake it around, so that couldn't have been the cause for bubbling to re-start.

Yesterday the sugar drops arrived so I bottled the beer, tasting a bit at the bottom, middle and top as I went. Bottom and middle were ok but the top couple of inches had an even more vinegary taste, definitely not just my imagination this time.

So now I'm wondering...
- is the cider now just sitting there turning into vinegar and that's causing the bubbling?
- if the bubbling is from vinegar production, why wouldn't the beer have also bubbled?
- was it relevant that I let air back through the lock, or was it just coincidental that the bubbling re-started about that time?
- is it likely that the vinegarization grows downward consistently enough that the bottles taken from the bottom and middle will be ok?
- in general, will bottle conditioning be able to do anything about acetobacter?

I think my sanitization is ok, I did a couple of other brews before this in the same manner and they were ok, but those I bottled within 48 hours of racking, not ten days.
 

hotbeer

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It might be that it wasn't finished fermenting and possibly getting your sample disturbed the bottom life enough to wake something up. How long has it been in the fermenter? Do you do SG checks to determine if it's ready? I'd never go by airlock bubbles to tell me when to bottle.

If it really is getting vinegary tasting, then I'd really suspect sanitation issues from the very start and not just the air that replaced the sample you took. Unless maybe that air also brought with it some of the airlock liquid that might have gotten infected.

Might get more attention from those that know about cider specific issues in the cider sub-forum. I've never peeked in there to see if it's mostly the same members or not. You have to scroll further down the main page to get there.
 

RolandD

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Acetobacter are in the air we breathe. It could have got in when you racked it or when you sampled. Another contributing factor was that you racked to a bottling bucket and let it sit for two weeks. This introduced oxygen which the acetobacter need to convert ethanol to acetic acid. Way too much head space for way too long. Even without turning to vinegar, your beer would probably have been oxidized.

Vinegar production can occur concurrent with alcohol production, which is, most likely why you had air lock activity.
 
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zppz

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Okay a little update. I went to take another sample from the tap and noticed that the bucket was very warm, so warm that the thermometer sticker was not reading anything so it must have been over 36C (98F). I hadn't noticed this for a while because there was a thermal jacket around the bucket so I couldn't see the meter, and I hadn't really been checking anyway.

Turns out that after a power cut, my raspberry pi controlled heating pad had turned on and stayed on. My program had not re-started after the reset, and the default pin state was to have the heating pad on. This would have accounted for most of the slow steady bubbling.

The vinegar-like taste of the cider from earlier might have been my imagination, because it was no longer present. There was a tiny bit of what might be lacto infection on the very top but I bottled it anyway just as an experiment. Strangely the taste was better at the top than at the bottom, opposite to how the beer was. I put sugar drops in the bottles but very little sign of carbonation after 4 days so hopefully no gushers.

On the other hand the beer bottles were super hard after just a week. I tried one of the beer and it's drinkable but has a slight plastic taste, perhaps from being in the plastic bucket for a month? It reminds me of the smell of a beach-ball or a plastic blow-up swimming toy. I use rainwater collected from my roof and filtered, so should be low chlorine, and I didn't get this with my first two batches that were only in the bucket for about 10 days. The plastic taste is in the batch that was not inadvertently over heated.

Depending on how these mature I'm kinda expecting to throw both of these batches down the drain eventually. From this I've learned not to start a brew unless I have everything needed for bottling ready to go, so that I can get it out of the plastic quicker. Also just completely unplug the heating pads when they're not actually being used...
 
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