Everyone Always Says the Air Lock is Not an Indicator of Fermentation...

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

wonderbread23

Well-Known Member
Joined
Apr 1, 2009
Messages
1,050
Reaction score
47
Location
Brooklyn
...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 don’t 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 pressure…et 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 it’s not bubbling, it seems like a pretty accurate indicator of activity.
 
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.
 
answered your question :D

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.
 
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.
 
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.
 
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.
 
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.
 
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.
 
An air lock will bubble if the pressure inside the bucket is greater than the pressure outside of the bucket (diffusion). Just because an air lock is not bubbling does not mean fermentaion is complete, it just meants that the rate has slowed and a pressure equilibrium has been reached on both sides of the membrane.
 
Bubbles do imply that fermentation has started but confusion sets in when people take that implication and try to make it an equation. They think, "If bubbles mean fermentation has started then no bubbles must mean fermentation has not started." But you can't make that logical assumption. Lack of bubbles has no bearing on if fermentation has started. Bubbles also don't mean fermentation is still going, only that at some point it has started.

So you are right that airlock activity is an indicator that fermentation has started.* What it is not is an indicator that fermentation has not started, an indication of the completeness of fermentation, or an indication of the level of fermentation.

* Even then, there are some limited examples where airlock activity can happen without fermentation starting due to atmospheric conditions, but we usually keep our wort in controlled enough environments for that to be a non-issue.
 
or my neighbors cat sneezed in the yard before I could drown it in Star San.

I have never seen anyone drown a cat in Star San. Please post a video. Make sure to properly commentate while doing the drowning.
 
* Even then, there are some limited examples where airlock activity can happen without fermentation starting due to atmospheric conditions, but we usually keep our wort in controlled enough environments for that to be a non-issue.

Do we really, in the typical household????

Often an airlock will bubble if the fermenter has been disturbed in some way, like a change in temperature, change in atmospheric pressure, the cat brushing against it, opening it up to take a hydro reading, any number of things. The co2 has sat in stasis for a period of time, then it was disturbed so it is not longer at equilibrium with everything else now. And therefore it is blipping in your airlock...

Or you could indeed have fermentation happening, since maybe your fermentation was laggy and a change in temp restarted fermentation.

Airlock bubbling only tells you that co2 is coming out of the airlock, it is not telling you why. And there's various reasons. That's why it's not a good idea to equate airlock bubbling with fermentation...It could be because it is fermenting, or it could not be because of fermentation...so That's why it's not a trustworthy tool.

And airlocks sometimes bubble or they don't. And airlock is a valve, a vent to release excess co2...NOT a fermentation gauge. It's important to make that distinction, or you'll be panicking everytime a an airlock doesn't bubble, or stops bubbling.

99.5% of the "Is my yeast dead because I see no signs of "activity" threads on here are about, lack of airlock activity, and equating that soely with fermentation.

And 99% of THOSE threads, when the OP actually takes a hydro reading, they get the exact same results as he did.....That's why we say over and over and over that an airlock is NOT an accurate indication of fermentation activity.

I subscribe to all the threads I answer, so I SEE the results of this everyday. I get the feedback, whether it's in the treads them selves OR in pms, the results are the same, taking airlock bubbling off the table get's responses like THIS thread posted today. A thread mind you which I had NOTHING to do with since I was baking 30 Jamaican Banana Breads while this thread went up yesterday....

Brewed up a batch of wit and pitched some Danstar.

24 hours later and nothing. No krausen, no airlock activity. Read a bunch of bad reviews about Munich and thought mine was bad. Waited a few days and still nothing. Thought about pitching some more, possibly something else and then remembered what experienced brewers always say....

"USE EVIDENCE BEFORE ACTION!"

took a gravity reading after 4 days and i had gone from 1.050 to 1.012. Damn, that's pretty much my target. There was never any krausen nor activity in the airlock. Checked my hydrometer in water and it's good.

So, happy brewing and I can join the club of always trusting objective findings over subjective. Thank's to all of you and your info on here.

Cheers and happy brewing! :mug:

Or this one....I could post hundreds of these to illustrate it...just from this week alone.

This happened to me on Friday with the same yeast on a wit. I had no krausen or airlock activity all weekend. OG was 1.050. Took a hydrometer reading on Monday because I was about to re-pitch and it was at 1.012. First time I have ever seen fermentation without ANY visible signs.

That's why I find these discussions utterly ridiculous. On here, on a daily basis we have PROOF that airlocks are not a RELIABLE indicator of anything else other than whether or not co2 is coming out of an airlock...And even less of an indicator of why it isn't.

And I STILL get a 50% airlock bubbling on my OWN fermentations.....But I have a 100% success rate on my fermentations. I've NEVER had to pitch new yeast in a batch of beer I brewed, regardless of what the airlock was doing.

Airlocks tell you the "what" or usually what's NOT happening...co2 being released, but not the why.....

A hydro reading tells the why....

I think part of why people rely on them or think they need to is cultural and had no bearing on brewing today.

Back in the bad old days, the predominant airlock was an s type...and often they were made of glass and sat relatively heavy in the grommet, and that's where people like papazain and those who influenced him got into the habit of counting bubbles...but now adays with 3 piecers being the norm, and most things being made crappy these days...it's just not a reliable means anymore.


The trouble is, that even the authors for the most part have been brewing so long that they don't pay attention to the airlock, yet the perpetuate the myth from the old days of bubbles meaning anything....though I figure, as a writer myself, they have long moved past the basic methodology that they wrote about...it's easy to do...to "preach" something very basic, while doing a process somewhat more complex...or like most of us who have been brewing awhile, taking shortcuts.

Co2 is heavier than air...there can be plenty of co2 going on, plenty of active fermentation happenning but there is not enough excess co2 rising or venting out to actually lift the plastic bubbler

The 3 piece airlock is the most fallable of them all, often there is simply not a strong enough escape of co2 to lift the bubbler. Or they can be weighted down with co2 bubbles, ir hteir is a leak in the grommet or the bucket seal, anynumber of factors.

If you push down on your bucket lid often you will suddenly get a huge amount of bubbling as you off gass the co2 that is there present but no needing to vent on it's own.

It's great if people's airlocks work for them, but it's not too hard to see on any given day here, proof that it's not the case for the rest of us brewers.
 
wat
Your blow-off tube doesn't bubble?;)

Not really, I get so worried that I usually sit in the corner and cry for a couple of weeks while the beer ferments...or does it?!?! :(

On my Barleywine my blowoff needed a blowoff:rockin:

Can't see the vid on this computer, but I remember the posting on the original thread. THAT was an active fermentation. BTW, did you take a hydrometer reading?? :p
 
Do we really, in the typical household????

Often an airlock will bubble if the fermenter has been disturbed in some way, like a change in temperature, change in atmospheric pressure, the cat brushing against it, opening it up to take a hydro reading, any number of things. The co2 has sat in stasis for a period of time, then it was disturbed so it is not longer at equilibrium with everything else now. And therefore it is blipping in your airlock...

I respect your advice, Revvy, but re-read my post. If fermentation hasn't started, there's not a whole lot excess of CO2 in solution.

Airlock bubbling only tells you that co2 is coming out of the airlock, it is not telling you why. And there's various reasons. That's why it's not a good idea to equate airlock bubbling with fermentation...It could be because it is fermenting, or it could not be because of fermentation...so That's why it's not a trustworthy tool.

And airlocks sometimes bubble or they don't. And airlock is a valve, a vent to release excess co2...NOT a fermentation gauge. It's important to make that distinction, or you'll be panicking everytime a an airlock doesn't bubble, or stops bubbling.

99.5% of the "Is my yeast dead because I see no signs of "activity" threads on here are about, lack of airlock activity, and equating that soely with fermentation.

And 99% of THOSE threads, when the OP actually takes a hydro reading, they get the exact same results as he did.....That's why we say over and over and over that an airlock is NOT an accurate indication of fermentation activity.

I subscribe to all the threads I answer, so I SEE the results of this everyday. I get the feedback, whether it's in the treads them selves OR in pms, the results are the same, taking airlock bubbling off the table get's responses like THIS thread posted today. A thread mind you which I had NOTHING to do with since I was baking 30 Jamaican Banana Breads while this thread went up yesterday....
(emphasis mine)

Once again, reread my post. I'm very specifically saying you can't equate airlock activity with fermentation. Implication is not equation. A -> B does not mean B -> A or !A -> !B. Your posts are invaluable to those beginning brewers who are concerned fermentation has not started but that's not the point I'm making here. If you haven't messed with your fermenter since you pitched your yeast and you see airlock activity, it's very safe to assume that at some point fermentation has started. That does not mean that if you don't see airlock activity, your beer is not fermenting.
 
I respect your advice, Revvy, but re-read my post. If fermentation hasn't started, there's not a whole lot excess of CO2 in solution.

(emphasis mine)

Once again, reread my post. I'm very specifically saying you can't equate airlock activity with fermentation. Implication is not equation. A -> B does not mean B -> A or !A -> !B. Your posts are invaluable to those beginning brewers who are concerned fermentation has not started but that's not the point I'm making here. If you haven't messed with your fermenter since you pitched your yeast and you see airlock activity, it's very safe to assume that at some point fermentation has started. That does not mean that if you don't see airlock activity, your beer is not fermenting.

I was agreeing with you about everything you posted except the "controlled environment" part of it.

...but we usually keep our wort in controlled enough environments for that to be a non-issue.

Most home breweries, at least those of folks just starting out aren't that controlled so any number of things can cause an airlock to be disturbed to either make it stop or start bubbling. I think the "Do you Poo near your Brew?" thread illustrates that folks on their first few batches (who usually start those kind of threads anyway) don't exactly have the perfect temp contolled "clean" room.

That's the only part of my post that really related to what you posted. The rest of it was in response to the rest of the thread.
 
As mentioned early on it is an indicator it just isn't a measurement.

But it's not even an indicator...plenty of times an airlock will start bubbling on a bucket immediately after you push down the lid, mere seconds after you pitch the yeast. And that's NOT even from co2 it's the o2 that we just pumped into the wort offgassing. Hell, when I use uso5 I sprinkle on my wort, let it hydrate of the surface for 15 minutes, then I lift my bucket up and move it in my closet, and the second I pick it up the airlock starts bubbling and may go on for 15-20 minutes then stop, just from being sloshed around...so again, how is a bubbling airlock a indicator, if it can bubble for other reasons....even when it SHOULD be bubbling from co2.

We can circle discuss this for hours, in fact we have...and it still comes back to the fact that sometimes airlocks blip, sometimes they don't, sometimes they start, sometimes they stop and start again...and it really doesn't matter.
 
Sure if you want to be completely anal and split hairs, you're right.

Under most conditions, a home brewer can look at an air lock and use it as an indicator of fermentation activity. One can rest assured that when it is rocking 2-3 times per second over a long period of time that fermentation is taking place.

I trust my yeast and all I need to see is it get started and the air lock is the indicator that I use to tell me that it has and it has never failed me.
 
Sure if you want to be completely anal and split hairs, you're right.

Under most conditions, a home brewer can look at an air lock and use it as an indicator of fermentation activity. One can rest assured that when it is rocking 2-3 times per second over a long period of time that fermentation is taking place.

And again over the I would say 15,000 of the 25,000 postcount on here answering all the threads about this, I can find enough instances to disprove it. That's the point....If an airlock even ONCE doesn't behave in a way that we think it should, then it can't be a reliable indicator of anything.

Like I said earlier if your airlock is working fine, enjoy the bubbles for what they are, entertainment....but don't rely on it to mean anything other than MAYBE some co2 is coming out......and that is tenuous as well, 'cause it could just as well be o2......


*shrug*

This is a boring discussion, like it has been the countless times someone starts it up again.
 
This thread is an indication of a particular kind of fermentation.

I didn't want to find any pictures of THAT kind, so I went for "hot air" instead. ;)

bottle.jpg
 
Back
Top