How Do I Know If Fermentation Is Complete?

Question:

I am fermenting a high gravity Belgian-style ale (original gravity= 1.103) that I moved into a secondary (carboy) after about 15 days.

It’s been about six weeks total now. When I racked the beer to the secondary, the gravity reading was 1.027 and the air lock was still doing about 3 bubbles every minute.

It’s been at about 72 degrees the whole time. When I check the air lock now, there is still a very regular pattern of one bubble every 2.5 minutes. I brewed a big beer like this before and waited for all air lock activity to stop before bottling – maybe 90 days – but I had carbonation problems.

Because of that, I am planning to add a dose of yeast to this beer whenever it is that I bottle it. My question is, how completely should bubbling in the air lock have stopped before I bottle? I don’t have a predicted final gravity with the recipe, but it is definitely less than one fourth of my original gravity at this point. Is there a rule of thumb for how little activity is enough to consider fermentation done?

Answer:

If you want to be sure it’s done, an accurate method is to take gravity readings. If the gravity doesn’t change over a certain time period, it’s most likely done.

High gravity beers can sometimes slowly drop a few points over longer than usual time periods, so you might want to take that into consideration when taking your readings and space them apart by several days.