Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > Everyone Always Says the Air Lock is Not an Indicator of Fermentation...
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Old 12-14-2010, 06:08 AM   #1
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Default Everyone Always Says the Air Lock is Not an Indicator of Fermentation...

...but why not? Okay, well maybe I'm being a bit fictitious. Before I get yelled at...

I get the fact that it is probably a bad indicator of fermentation being complete since CO2 production can slow quite a bit towards the end and become so slight that the CO2 that is evolving goes unnoticed. This can lead to early bottling, drinking under-attenuated beer, and drinking beer that is probably not as good as it could have been. It is probably also a bad indicator of the start of fermentation since the time lags created during the reproductive phases of fermentation as well as the temperature of the ferment will cause the time from pitch to bubbling to vary. These reasons are probably enough to discourage hyper-active new brewers from eagerly ogling their airlocks for changes in an attempt to find meaning in the bubbles.

That being said, I propose that instead of blindly accepting the phrase in the title of this topic, we instead use the airlock as a practical tool to tell us that the main stages of fermentation are taking place...especially on buckets were active fermentation cannot be easily viewed. I want to get some ideas from those who are likely smarter than myself on the topic to make sure my logic / scientific understanding is sound.

The basic formula describing ethanol fermentation is:

Glucose → Ethanol + Carbon Dioxide
C6H12O6 → 2C2H5OH + 2CO2

With the basic pathway described above, I donít see how ethanol could be getting produced by yeast without a proportional amount of CO2 being produced. In theory the amount of bubbling would be proportional to the amount of ethanol being produced. During the cell reproduction phases, little CO2 is being produced, hence no increase in pressure and no bubbles. Once active fermentation starts however, there should certainly be some bubbling. Depending on the temperature of the fermenting beer, the time it takes for this will vary, but at some point it will hit the saturation levels for CO2 that the liquid can withhold and start off-gassing, increasing the fermentation pressureÖet voila bubbling.

Short of not having an adequate seal between the air lock and bucket (or lid, or grommet, or bung) I cannot see anyway possible that it would not bubble. If you know the rules, and possible reasons why itís not bubbling, it seems like a pretty accurate indicator of activity.


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Old 12-14-2010, 06:11 AM   #2
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I think the point of the phrase is that it's not the end-all-be-all indicator of what's going on with your beer. It's not a meter. It's just an airlock. The trouble is that people get to depend on it to the point where I've seen people trying to equate bubbles per minute to mean a certain number on some fermentation scale they're devised. "I'm down to 5 bubbles per minute, that means I can bottle in 37 hours!" sort of things.

The hydrometer is really the only way to know for sure what's happening. But yeah, the airlock is a good basic indicator that something is happening. That's all.


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Old 12-14-2010, 06:12 AM   #3
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You can also get off gassing from temperature changes as the CO2 drops out of solution.
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Old 12-14-2010, 06:15 AM   #4
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Quote:
Originally Posted by wonderbread23 View Post
Short of not having an adequate seal between the air lock and bucket (or lid, or grommet, or bung)
answered your question
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Old 12-14-2010, 06:22 AM   #5
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Quote:
Originally Posted by AZ_IPA View Post
answered your question
Yeah, I'm guessing the leak is quite common. It just seems kinda lame to completely dismiss it off-hand when a lot of brewers post about lack of activity.

Disclaimer: I use mine all the time as a tool in conjunction with visual observation of the beer. It basically tells me where the beer is at, when to increase the fermenter temp to encourage complete fermentation, and when to crash it at the end.
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Old 12-14-2010, 06:49 AM   #6
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I gauge the fermentation off of the bubbles. When I no longer see them going i know I can start with the hydrometer to get something accurate.
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Old 12-14-2010, 07:04 AM   #7
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I started brewing way back before Al invented the internets and I did not have access to all this good information. In those stone age days, we liked to see bubbles. Bubbles were good, and generally indicated good beer a-brewing.

Now, enlightened as such, I have a hell of a lot more to worry about as far as correct pitching rate of yeast, if my fermenter is a degree too hot or cold, my sanitizer solution was a few points off, wort was exposed to a germ, my grain was crushed a bit coarse and early, my dishwasher had a noodle stuck in the drain that gave me "the infection", or my neighbors cat sneezed in the yard before I could drown it in Star San.

Beer is tasting about the same but I had no clue what I was missing worrying about before the internets came along, now I know.
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Old 12-14-2010, 12:28 PM   #8
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I use the airlock to tell me where the beer is in it's cycle. I've done enough to know when it is probably done and just out-gassing, or still going. I will never bottle without taking an hydrometer reading, but I don't like to open an actively fermenting beer just to take a reading.

...... I've only ever had one time when this let me down. I pitched Notty, and didn't see any activity on day 1. Called Danstar to see if there was any problem with the yeast. Day 2 nothing, started panicing, wondering whether to pitch another yeast. Day 3 still nothing; checked gravity, and the beer was done. I had rigged up an elaborate airlock system to try and capture any blow-off yeast (which there wasn't any), and obviously had an air leak. Never messed with it again; just properly affix an airlock.
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Old 12-14-2010, 12:44 PM   #9
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Buckets leak, airlocks don't bubble. Shine a flashlight onto the bucket lid & you'll see the shadow of the krausen (or the ring it left behind). Then relax &let the yeast finish.
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Old 12-14-2010, 12:54 PM   #10
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IMO there are lots of observations one can make and seeing the airlock bubble is just one of them. You have to know how to interpret the information and it's usually just qualitative information but it's not like this is some super complex thing (a fermenter with an airlock). Often the "airlock is not an indicator..." mantra is meant for beginner brewers but gets propagated as if it's some sort of crime. There is a little bit of info to be had from an airlock bubbling, ignore it or not, your choice.


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