I did a BIAB (simple Pale Ale) 5 gallon batch three weeks ago. After a week in the primary, the SG was 1.010 (about where it should have been). I transferred to a secondary and it’s been there for two weeks. I have activity in the airlock. Is it just CO2 escaping or did I transfer from the primary before the fermentation was complete?
I have another batch (Porter) and the airlock on the secondary is quiet.
The best way to confirm that fermentation is complete is by taking gravity readings over a 2-3 day period. If the S.G. remains constant, then you know it’s complete. Airlock activity could be from escaping CO2, as you pointed out. I’ve only been brewing for about 8 months and I always have to remind myself to ignore the airlock and test the S.G. too. Good luck!
There’s more to yeast than converting sugar to alcohol. One is acetaldehyde. It gives beer a green apple flavor. If it’s real strong it can smell and taste like a latex exam glove. Gravity can be bottomed out but it may still need time for the yeast to finish converting these monsters to good stuff. Most folks don’t use a secondary anymore. Your test should be for stable terminal gravity but also odor and taste tested that acetaldehyde is gone. For me that’s usually three to four weeks.
It’s pretty common to see bubbles after fermentation is done because of escaping CO2, but you can’t be sure without taking the gravity. I leave it in primary for about a week after fermentation finishes.
Agreed on taking hydrometer readings - 3 identical readings over successive days and you can be confident that fermentation is done. Unless I’m making a wheat beer I rarely keg a beer in under a month. As Jim said, leaving a beer on the yeast a little past the point fermentation stops will let the yeast, in essence, clean up after itself by getting rid of off flavors/aromas that often end up in beer if you rush things. Unless you make a very high OG beer, a fruit beer, or choose to dry hop in secondary (I do), racking to secondary is not necessary, and can be detrimental.