Air bubbles after fermentation is done

I hate to beat a dead horse, and I know how many threads there have been about "Is my fermentation done?" or "It's taking too long, is there something wrong?".

I brewed an Irish Red a few weeks ago, and fermentation seemed to go great. Used a large starter and saw activity in less that 12 hours. At about a week the bubbles were once every 20-30 seconds and they stayed at that rate for another week. I took a gravity reading over that last week and the wort was clear and there was virtually no drop in gravity.

My question is where is the C02 coming from?

Is is possible for fermentation to be done and the airlock still show activity?

Sure, it's possible for co2 to continue to off-gas after fermentation is over. That's perfectly normal.

If you want to see it really go crazy, take it from a cooler place to a warmer place! When I have some ales cold conditioning a bit after fermentation, and I bring them out to the kitchen to get ready to keg or bottle, the airlock goes crazy! The reason is simply that cooler liquids "hold" co2 better, and when I move it to a warmer place, it bubbles quite a bit as the co2 is released.

Temperature changes and weather changes (like a rise in barometric pressure) can cause this, and so can moving the fermenter.

Trust your hydrometer.

If the temp of the wort changes, you can see bubbles coming out the airlock as CO2 is released. You've probably also noticed it bubbles when you move it, because CO2 comes out of solution.

You want a stable hydro reading over the course of a few days. If you have that, then you're fine. Don't worry about the airlock.


Edit: Beaten by a minute!