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Home Brew Forums > Home Brewing Beer > General Techniques > Trust Your Airlock
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Old 08-31-2009, 05:46 PM   #1
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Default Trust Your Airlock

If your fermentor doesn’t leak and you keep it at a constant temperature, airlock activity absolutely is a sign of fermentation. The term “off-gassing” is sometimes misused. If the temperature of finished beer goes up it will off-gas CO2 through the airlock. Also, thermal expansion will push gasses out of the airlock of finished or unfinished beer. If the temperature remains constant, the CO2 rich and neutral pressure environment in the head space of finished beer will allow it to hold onto the CO2 that is in suspension indefinitely. Under these controlled conditions, if you have airlock activity, you still have fermentation going on (it may be an infection, but still it’s still fermentation. ) The reverse is also true. With no leaks or temperature changes a lack of airlock activity means your yeast is finished or never started to begin with.

Hydrometers are sometimes nothing more than an excuse for us noobs to play with our beer. You really only need three readings. One pre-boil to confirm your mash/lauter efficiency (so that you can make hop adjustments.) Another before fermentation, and the last before bottling to confirm attenuation. If you leave your beer in the primary for a few weeks at the proper temperature and you pitched health yeast in the correct amount into well oxygenated wort, your beer is finished if airlock activity has stopped for several days in a row after that time (run-on sentence, sorry.) Another hydrometer reading should not be necessary (edit: after this one if it determined that your beer was finished . . . but it might be if your beer hasn't fully attenuated.)

Yeah, we've had that stubborn saison, but . . . trust your airlock!


So science people, is this so wrong?
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Reason: trying to be more clear.
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Old 08-31-2009, 05:50 PM   #2
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Yup, I have had the occasional leaky bucket or carboy cap but 99% of the time airlock activity matches the hydrometer.

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Old 08-31-2009, 05:56 PM   #3
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so you are so pissed at me that what, you are going to start one of these threads for each of the things that I have written about???

Jesus man, it THOUGHT the discussion in the other thread was all in good spirit, even the jesting....I've always thought you were a great guy and have always respected you, AND thought that last discussion was in good sport.....I'm sorry if I hurt your feelings, dude.

But geez this is pretty transparent.....

You gonna start timing your bottle carbonations to see if 3 weeks at 70 degrees is wrong too???

Oy Veh.....

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Old 08-31-2009, 06:03 PM   #4
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The conditionals you mention (completely sealed fermenter, zero temperature fluctuation) make your statements valid, Herm.

However, in practice, these conditions are extremely difficult to meet under most circumstances.

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Old 08-31-2009, 06:07 PM   #5
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I'm sorry if I hurt your feelings
You flatter yourself. No feeling hurt, just the pursuit of accurate information for those with questions. This has been a thought that has come to mind every time the topic comes up. (And it does come up often.)
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Old 08-31-2009, 06:15 PM   #6
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Quote:
Originally Posted by AnOldUR View Post
If your fermentor doesn’t leak and you keep it at a constant temperature, airlock activity absolutely is a sign of fermentation. The term “off-gassing” is sometimes misused. If the temperature of finished beer goes up it will off-gas CO2 through the airlock. Also, thermal expansion will push gasses out of the airlock of finished or unfinished beer. If the temperature remains constant, the CO2 rich and neutral pressure environment in the head space of finished beer will allow it to hold onto the CO2 that is in suspension indefinitely. Under these controlled conditions, if you have airlock activity, you still have fermentation going on (it may be an infection, but still it’s still fermentation. ) The reverse is also true. With no leaks or temperature changes a lack of airlock activity means your yeast is finished or never started to begin with.

Hydrometers are sometimes nothing more than an excuse for us noobs to play with our beer. You really only need three readings. One pre-boil to confirm your mash/lauter efficiency (so that you can make hop adjustments.) Another before fermentation, and the last before bottling to confirm attenuation. If you leave your beer in the primary for a few weeks at the proper temperature and you pitched health yeast in the correct amount into well oxygenated wort, your beer is finished if airlock activity has stopped for several days in a row after that time (run-on sentence, sorry.) Another hydrometer reading should not be necessary.

Yeah, we've had that stubborn saison, but . . . trust your airlock!


So science people, is this so wrong?
I havn't seen a single bubble from my airlock (which would indicate "airlock activity") from my Oktoberfest primary in 5 days (and i've looked enough) and in those 5 days my beer has gone from a 1.026 (after 2 weeks) to a 1.020 SG (after 2 weeks, 5 days). If, for some reason, there has been activity and I have just missed it (unlucky) then I still feel comfortable about using my hydrometer as my gauge because I am not going to waste anymore time than I already have by staring at the airlock to try to catch a glimpse of the odd bubble (activity). Although I have not met your "few weeks" mark prior to taking a final reading this would seem to indicate that airlock activity or lack of activity does not necesarrily, by itself, indicate whether or not fermentation is taking place. I am not sure I understand why anyone would argue overuse of the proper tool for the job. Not all beers require a 'few weeks" to finish fermentation. Besides...playing with the beer is at least 50% of why I choose homebrewing as a hobby. The other half...yum...and....
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Old 08-31-2009, 06:16 PM   #7
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Originally Posted by flyangler18 View Post
However, in practice, these conditions are extremely difficult to meet under most circumstances.
I agree. Especially for beginners. But a carboy in a fermentation chamber will come pretty close most of the time. Even my basement temperatures are constant enough that I trust the airlock.

The truth is that a blanket statement either way can be misleading and out of place.
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Old 08-31-2009, 06:21 PM   #8
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If the fermenter is completely sealed and the temperature is constant without fluctuation, the airlock will bubble during fermentation.

If it isn't, you have a leak somewhere.

You can indeed use the activity of the airlock as an indication of fermentation if you recognize that its accuracy is subject to outside variables like those listed above, and the only 100% accurate way to determine completion is using a tool like the hydrometer or refractometer. Excessive sampling does nothing.

You have to know the limitations.

By way of example: my Mild is constantly on tap at the house, and as such, I often have a batch 'in process'. I've brewed this recipe enough times using the same yeast or by introducing a single variable that I can tell from experience that two weeks from pitching and it is ready to go, on the button for calculated FG. If I'm experimenting with a new strain, out comes the hydrometer to log the ferment. I test my intuition from time to time using the hydrometer, but I can recognize completeness by visually inspecting the beer in the carboy. I don't use an airlock except in rare circumstances.
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Old 08-31-2009, 06:49 PM   #9
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There can be fermentation without airlock activity in a perfectly sealed vessel. The co2 will no escape through the airlock until all the deadspace is filled. Hour many hours of fermentation is that before it's filled? So yes you can have fermentation before airlock activity. You cannot translate theory into practice. The hydrometer PROVES without a doubt something has happened. Airlock only proves a change in pressure. You can have airlock activity froma drastic temp change without any actual fermentation. So yes, this is so wrong.

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Old 08-31-2009, 06:52 PM   #10
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One could also argue that just because fermentation has stopped, that does not mean that your fermentation is complete. There are so many variables that I would never simply trust my airlock to think "oh, it's done."

Often I don't check my FG using the hydrometer for the "drinking" beers, but that's because I had a high pitching rate, the proper temperature, plenty of agitation and let the beer sit for a long time.

New people that are waiting "7 days" to rack to secondary or even bottle should ensure that their beer is ready.

So while brewing is as much an art as it is a science, you cannot absolutely know where your beer is at without sampling it. You can practice brewing this way, you are simply not getting all the information you could otherwise.

Not to mention that fermentation completing does not necessarily mean the beer is ready. There is still flocculation, clearing, conditioning, etc.

Bottom line: Why not grab a sample, take a reading and a have a taste??? One of the most enjoyable experiences in homebrewing is tasting the beer at every stage and it literally takes 3 minutes.

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