Wort back from the dead?!?

[caligula]

Next installment in my bizarre belgian wit saga.

I asked a question about my wit that seemed to have not finished fermenting:

My starting gravity was 1.055. The airlock bubbled for a day or so and then stopped (yes, I know this isn't a reliable indicator of anything). After about 3 days I took another reading, and got 1.027. Now a few days later I'm still at or very close to that gravity. This seems high to be finished at considering my starting gravity.

The consensus was to rdwhahb and let it ferment another week. I did, and was then going to bottle it. Unfortunately I got busy and let it sit. Now it's been about 3 weeks. There was no bubbling in the airlock after about day 2 and the CO2 pressure didn't even seem to be that high in the 3 piece airlock.

Now, this morning, suddenly the fermenter is bubbling, CO2 pressure is up to normal. What the hell?

Can yeast suddenly come back to life and start fermenting or does this indicate a potential wild yeast infection has taken hold?

The only change in the room was that I left the A/C on a little low last night and it was probably 65-68 in the room. I don't see how that could cause anything.

 

[Revvy]

Any number if things can cause the airlock to bubble, most of them having nothing to do with actual yeast starting or stopping it. Evironmental changes in a room like you describe is one of them...It can both just cause a change in the pressure in a fermenter and cause co2 trapped in the trub to be released or out of solution, or the yeast can wake up. But the why can't be known only the what unless you take a gravity reading.

All you know is something is happening (your airlock is bubbling) but you don't know why....An airlock is just a vent to release excess co2, it's not a magic fementation gauge....

 

[edmanster]

Me and SWMBO noticed this also.. Fermentation was done for about a week and just clearing up.. We had one of the best days we've seen this year on saturday.. I thought that the house just warmed up a little and caused a little airlock activity. Well we had a low pressure system pushing in and it snowed 4" over night.. Im assuming it was the change in temps and with the storm coming in caused it..

 

[quadbikerjosh]

i think barametric pressure thus corelating to atmospheric pressure differences could have an impact on the release of trapped co2. it could explain this. ive noticed a corelation between how fast my air lock bubbles and weather or not theres a storm coming in, even tho the temp doesent change in my apartment. i could have a bubble every other muinute at the very end of a ferment, and a storm will come in and it will pick up a noticeable amount, although gravity readings have stayed practically the same.

 

[jfowler1]

It looks like I joined the party a little late.

The simple answer is, no, fermentation has not restarted.

As already mentioned, the bubbling you see is due to the expansion and contraction of gases as temperatures move around.

I used to explain the bubbling that would restart when a brewer increased temperature as CO2 leaving the solution and exiting the airlock, because we all know that the beer can be saturated with more CO2 during fermentation at lower temperatures, and will absorb less CO2 during fermentation at higher temperatures. Similarly, it is why you risk suckback through a blowoff or air lock when you crash cool a carboy (the contraction of gas and reabsorption into the liquid creating the opposite effect of your "zombie" yeast). This explains why it takes cool lagers more time to show "signs" (bubbling) of fermentation as compared to an ale. It also explains why you need to know the temperature of your beer before you calculate how much sugar is needed to prime and bottle. Again, warmer beer has less CO2 in solution, cold beer has more CO2 in solution.

I was corrected that it is not just CO2 in beer that experiences this effect. Another member pointed out that you will see a similar effect if you put an airlock on an empty carboy and heat it up - it should bubble. Similarly, cap an empty 2 liter soda bottle and throw it in the freezer - it should contract.

It is simply the property of gases at work - not yeast back from the dead....

...at least, lets hope it isn't yeast back from the dead.

Joe

 

[Flywheel]

I really hope it is back from the dead, then you can play this for your yeast.

 

[AKnewbrews]

My last Belgian Wit yeast started off great, then it slowed but steadied, and took a month to drop down low enough for me to say "ok, let rack to secondary on the Pomegranate" The yeast never went dormant, it just kept going and going and going. I took too many gravity readings and lost beer to it. Every 3 days it would drop 3 to 5 points. I finally left it after the 4th gravity check and just let it go for over a month until it looked like there wasn't any activity left. Then checked it and it dropped down to 1.005 after the fruit addition. That batch took over 2 months for primary and secondary to finish before I could even think about bottling.