Signs fermentation is complete, are airlock bubbles enough to tell?


I have read in several places that two identical specific gravity readings over an interval of 24 hours means it is time to stop fermentation. This means opening your vessel once a day to check and risk introducing nasty bacteria. My question is can you use the rate of bubbles in your air lock to tell it’s time to stop fermentation ?


It’s not necessary to watch your beer like a hawk - even after fermentation is complete the yeast are still busy cleaning up your beer. For regular strength beers (<1.054), simply leave the beer for a week before even thinking of opening it.

You’ll find some great answers to this and other homebrew questions on

[Just for guidance, the question might be a little off-topic for this forum since it’s not specifically about brewpi. There are many good general homebrewing forums, such as homebrewtalk where you’ll be better served for this kind of question. :smile: ]

Everything I had read seemed quite dogmatic about checking it every day, so I assumed bad things would happen if I wasn’t on the ball. I am relieved to hear I can be more relaxed with it.

Sorry, your right, it is off topic but the problem is you guys are just so helpful and straight up with your answers. I find it a rare thing these days.


I disagree with @mdma about this being off-topic actually, I think general brewing questions are very welcome. As my answer will actually involve some BrewPi related content :slight_smile: But he is right that you might get an answer quicker on stackexchange.

I don’t take many gravity readings myself, I just listen to the bubble rate. Of course I take the SG and the FG, but in between I would rather not open the carboy: @mdma is right, just leave it, don’t rush your brew.

To clarify: I don’t listen to the bubble rate to determine when it is done, I listen to it to adjust my temperature. You can find a flavor profile for most yeasts that tells you which flavors are created at low and high temperature. At high temperatures you get more esters, or fruitiness. If you don’t want that and want a cleaner taste, you will want to keep the temperature low, but not so low that the yeast will go dormant. The bubble rate can help you out there.

When you get a stream of bubbles, feel free to ramp the temperature down. But when the yeast has consumed most of the simple sugars, it will need a higher temperature to stay active. So when the bubble rate is dropping to below once every 3 seconds, slowly start increasing the temperature again towards the high end of the yeast temperature range.

For a hefeweizen, I start around 20 until it is bubbling happily, then lower the temperature over 1-2 days to 16-17 degrees. I keep it there until the bubble rate is slowing down and then I do a ramp to 22 degrees over 4-5 days. Finally I keep it at 22 for 2 days.

By then, I take a gravity reading. If it is at my expected SG, I sometimes bottle and sometimes I do the right thing and I check again 2 days later. That’s the safest path to prevent bottle bombs and why it is advised everywhere. But there is no point in checking the SG before you suspect it to be done.

1 Like

Actually I’m the one who’s sorry! :blush: The forum is growing and being defined - I wasn’t sure what is OT and not. Thanks for the question, I’m glad we could answer it for you, please keep 'em coming! :slight_smile:

For a dumbass like me it would be really useful to maybe have a guide or tips on getting the most out of Brewpi.

@Elco I’m not sure if it’s the yeast I tend to use safale U.S.-05 but I can’t find anything that indicates the flavours you might get at different temps. Do you have a resource you get these from?

I have never used Safale, I always use Wyeast. But from what I have read Safale 05 is a very clean yeast, so it might not respond as much to temperature as other strains. The general less esters at lower temperatures still applies though.

S-05 should be clean and should be more forgiving, but I agree with Elco that usually the lower temperature in the nominal range the fewer esters you should get. This assumes you have enough yeast though. However, this shouldn’t be an issue with dry yeast for most typical gravity beers.

The best part of the brewpi for me are the profiles. I’m pretty aggressive with my temperature control. I let the beer go roughly 2 days with either a constant temperature or a minimal rise. After that the beer should already be at high krausen with the growth period complete and a significant portion of the fermentation already done. I then ramp the temperature to a higher temperature to help the yeast finish the beer out while staying happy and cleaning it up (diacetyl rest). Here’s my standard ale profile. You can add more time on the backend as necessary before chilling (something like a RIS would need more time). I only check my gravity at the start and then finish.

Day Temp
0 65F
2 67F
5 70F
10 73F
14 60F

1 Like

I typically use brewpi to see what my yeast is doing. Like previous posts, follow the yeasts guidelines on temperature. Pitch and hold the initial temperature. For Safale 05 I’d probably start around 65-68f. And prepare the profile to hold it there for 3-4 days. Here you can start to watch your graph and pay attention to what’s going on. If you have a decent chamber set up you can see that for the first 5-7 days you’ll almost never see the heater fire up. Because the yeast is making all the heat you need. As time passes, you’ll notice that the heater has to come on more and more to keep up the temperature. If it’s just a simple ale yeast like you’re using running the whole time at 65-68 is perfectly fine. You can watch the bubbles if you want and correlate this data to see how nice it is to log your temps along the way. After you notice the yeast aren’t producing their own heat for a few days you can either take a gravity reading to see that you are nearly done or just bring the temp up to around 72 for a couple days to help the yeast “clean up”

Wow thanks guys. All good advise. So is there any harm in leaving it 2 weeks or even 3 ? Rather than the 7-10 that seems common.

You can leave it in at temperature for a couple months if you like. I like to get the beer off the yeast and chilled in a keg, but there’s no harm in leaving it in longer. Eventually you’d have to worry about autolysis, but it takes a while. The reason I hurry it is that once the beer is fermented and cleaned up there’s nothing good that can happen at that point.

OK all understood, I think I have a more rounded feel for it now. Thanks again for all the advice.