How Do I Know If Fermentation Is Complete?


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?


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.