What is your longest active fermentation?

I've had wheat beer fermentations with airlocks bubbling for over 10 days. I've had baltic porter fermentations (using lager yeast) where the airlock activity went for about 9 days, but the gravity continued to drop over the course of 6+ weeks.

 

Yeast will do what yeast will do. It is not necessarily a bad sign. I suggest waiting another week or so and checking the gravity twice a couple of days apart to see if fermentation is complete.

 

I've had some brett beers chug pretty good for a month, 2 weeks for a lager, 10 days or so for a couple of ales when the basement was a little cool. They all turned out fine; just let the yeast do its thing.

 

I have had Saisons and Imperial IPA's fermenting for 6 weeks. Used yeasts with high attenuation, but tthey took awhile to get there

 

My lambic barrel had its first birthday back in August. What was there was good, but no real sourness had gotten started yet. It will be going for many months to come.

 

I also did an imperial red last year that went 8 weeks and still overcarbed 1/2 the bottles a couple of months later. I would have sworn it was done when I bottled, but it made a liar out of me.

 

I had one that was destined to be a sour (RR Consecration clone) that was pretty active for almost a month.
A pale ale I did not long ago was active for 3 weeks, and dropped a couple points from day 21 to 24. At 28 it had been stable those four days so I bottled it (needed it for 2 weeks later.)

 

I brewed a Belgian strong dark ale, around 1.100 OG that took 5 weeks, when it got to ~1.030 I had to raise the internal temp to around 75 to get it to finish.

 

Airlock activity may not correlate to fermentation activity. Co2 could just be releasing through the airlock.