Primary fermentation stopped, then restarted?

[wordswithtim]

Hey guys (and gals),

Question for the brains trust. Was fermenting a partial grain dopplebock. It seemed to ferment just fine. Gravity settled. I waited a few more days. Added finnings, waited 48 hours, then waited 48 more. Was thinking about bottling in the next few days when I was downstairs and heard the telltale 'blub blub' of gas escaping the airlock. After a bit of investigation there is definitely positive pressure back in the fermenter. So my question is, is it possible for fermentation to stop/start like that, or something more sinister going on? Never had this happen before. Any one else ?

As always, thanks for commenting.

 

[Gnomebrewer]

It is quite common for fermentation to start up again, especially with yeasts know for dropping out early (if they get stirred up again). It is unlikely after adding finings though (even more unlikely if you chilled before fining).

The airlock isn't a reliable indicator of fermentation - changes in temperature or movement of the fermenter can also cause gas to escape, making the airlock 'blub blub'.

Most likely scenario - it's just airlock activity with no fermentation. Of course, it could also be contamination (this is also unlikely if you followed good sanitation procedures).

 

[CJ-3]

I agree with Gnomebrewer. More than likely it is not that your fermentation started up again, but your homebrew is just offgassing some CO2.

The only reliable way to know that fermentation is completed is measuring gravity with a hydrometer.

 

[wordswithtim]

Thanks guys. Shall wait till it shuts down again and do another gravity reading. Appreciate it.

 

[Subdivisions]

Thanks guys. Shall wait till it shuts down again and do another gravity reading. Appreciate it.

Why wait? Take a measurement. There's a crapload of CO2 suspended in your beer from fermentation. It'll keep bubbling out even when the beer is finished. This happens mainly from temperature or atmospheric pressure changes or even just jostling the fermenter a little bit.