Why is the rule zero bubbles for 3 days rather than just 1 day?

[NeverDie]

Does fermentation sometimes restart itself after a day with no bubbles or something?

The rule of thumb I've heard is zero bubbles through the airlock for 3 days in a row marks the end of primary fermentation. If that's wrong, someone please correct me.

Anyhow, I figure this should be easy to automatically monitor with a bubble detector, such as on the OP of my other thread: https://www.homebrewtalk.com/forum/...al-emitted-weight-of-fermentation-co2.660586/

 

[deadwolfbones]

The only real rule of thumb is a constant hydrometer/refractometer reading for several days in a row. Airlock activity is too unreliable.

(Even constant gravity readings aren't necessarily foolproof for stall-prone yeast.)

 

[kh54s10]

If you had bubbles, having the bubbles stop will, more than likely mean that your fermentation is NEARING the end. It could still take several days to fully finish You can have a perfect fermentation and never see any bubbles. Especially if you are using a bucket fermenter. The lids are notorious for leaking.

Forget about the bubbles and get a hydrometer and learn to use it.

 

[NeverDie]

Forget about the bubbles and get a hydrometer and learn to use it.

Right. Got one of those. However, this is the automation forum. Unless you're proposing a tilt or similar... Anyway, leaking buckets are a separate issue and aren't my concern.

Besides, I don't get it: if you rule out a leaking bucket, how can you have a perfect fermentation and yet never get any bubbles through the air lock?

 

[deadwolfbones]

Right. Got one of those. However, this is the automation forum. Leaking buckets aren't my concern.

Whoops, sorry! Didn't notice the forum, was just looking at new posts.

 

[NeverDie]

Whoops, sorry! Didn't notice the forum, was just looking at new posts.

No problem. You get bonus points though if you can answer how it is that a perfect fermentation can happen without producing any bubbles through an airlock during a primary fermentation, assuming no leaks. That one has me stumped.

And you get extreme bonus points if you can figure an automated way to detect the end of primary fermentation (something other than using a TILT that is).

 

[Blazinlow86]

Not sure your question is written correctly. Are you asking if it's possible to have outgassing in a perfectly sealed container? Or are you referring to the other post that says it's not uncommon to not see bubbles especially when using a bucket as there notoriously leaky?

 

[kh54s10]

It still doesn't really matter. Even with automation bubbles in an airlock only means that more co2 is being produced than the vessel can hold. A slower fermentation may take more than 3 days to finish after bubbles stop. Not to mention stalled fermentations. Yeast don't work on a time schedule. Different yeasts will ferment at different speeds. The recipe can also have an effect on how long a fermentation takes. Temperature will also have an affect. Colder = slower in most cases.

The only way to be sure is to take gravity readings.

 

[Blazinlow86]

I was gonna say if you ever figure out any way let alone automated to detect when fermentation is done without taking samples let the brewing world know. It'll save us all alot of time

 

[S-Met]

Does fermentation sometimes restart itself after a day with no bubbles or something?

Yes, sometimes.

But bubbles are not reliable eve in a sealed container and here's why:
Fermentation is exothermic and heat causes gas to expand. As temperature begins to equalize, especially in temperature controlled environments, the liquid cooling causes a contraction of gas that slows down the airlock activity. Gas must be generated at a rate that is able to displace the volume of headspace in the fermenter and overcome the surface tension in the airlock, otherwise gas may stay in suspension within the fermenter. This may hint that fermentation is slowing, but does not mean that it is complete. In fact, fermentation may continue for an indeterminate time. A specific measurement tool is required, and even with said tool, guidelines correction factors may still need to be used to verify.

 

[NeverDie]

Yes, sometimes.

But bubbles are not reliable eve in a sealed container and here's why:
Fermentation is exothermic and heat causes gas to expand. As temperature begins to equalize, especially in temperature controlled environments, the liquid cooling causes a contraction of gas that slows down the airlock activity. Gas must be generated at a rate that is able to displace the volume of headspace in the fermenter and overcome the surface tension in the airlock, otherwise gas may stay in suspension within the fermenter. This may hint that fermentation is slowing, but does not mean that it is complete. In fact, fermentation may continue for an indeterminate time. A specific measurement tool is required, and even with said tool, guidelines correction factors may still need to be used to verify.

OK, so how about this: no bubbles *and* no decrease in must temperature for 3 days? I mean, yes, I suppose there might remain some vanishingly small traces of fermentation still happening that wouldn't register, but for all practical purposes...?

 

[S-Met]

OK, so how about this: no bubbles *and* no decrease in must temperature for 3 days? I mean, yes, I suppose there might remain some vanishingly small traces of fermentation still happening that wouldn't register, but for all practical purposes...?

How about this:
You're running a fever, how do you know its done? Wait an arbitrary 1-2 days or take your temperature?
You have an infection and your doc gives you 10 days of antibiotics. You feel better after 3. Do you stop the meds @3? Wait for 5? Or follow the orders? Cutting it short may cost you dearly.

Why would you skip out on a simple measurement (hydrometer or refractometer) just like the pros use in exchange for a variable and inconsistent system (bubble counter) and/or an arbitrary systemic belief that bubbles = fermentation? You are reinventing a wheel, replacing a round for a rectangle.

And if you were paying attention, stable temperature and lack bubble activity only means a state of equilibrium. Or a systematic leak.

If you choose to ignore the advice, its absolutely your choice. To be honest, I don't always take gravity readings. I know my appropriate sg, estimated fg and let ciders/wines or bold brews sit for a little aging. But airlock has never been an indicator. You may as well empirically say, fermentation takes 7 days, but wait 10 just incase. And if you bottle, hope you don't prematurely stall or you have a glass grenade.

 

[balrog]

I have seen somewhere the CdS-electric eye cells reading airlock bubble counter setup. Don't recall where. It was too dependent on measuring bubbles, which are byproduct of fermentation, temp variation, air pressure weather changes, leaky bung/bucket/airlock.

For me.

 

[S-Met]

Not to mention, airlock bubbles size and frequency are also dependent on the liquid volume in the airlock. Higher or lower volume means smaller ir larger bubbles. Some vigorous fermentations can halt airlock activity for short periods by exceeding the threshold of the airlock. Meaning it can pin the airlock to the top to freely expell gas. Its akin to a prv giving short bursts vs being wide open.

Back to airlock liquid. This liquid is evaporating depending on the external factors (temp humidity) and rate of airlock activity increases the rate of evap. Meaning two identical airlocks both filled with identical fluid and maintained in identical conditions with the exception of one on an active ferment and the other being a control: your control group should lose less fluid than the active airlock. This suggests that you will have more bubble frequency at the start than at the end since the volume of gas required to move the airlock is greater - unless you are maintaining a constant airlock liquid volume.

Also, a relevant concern is gas suspended in solution. Fermentation may be long complete but airlock activity is still occurring as gas is released from solution.

 

[kh54s10]

My present beer stopped bubbling after 3 days. 7 days later I took a gravity reading when dry hopping. It was too high. I swirled the bucket. Today I will take a gravity reading to see if it dropped. If not I will add some more yeast and wait another couple of days.

3 days after the bubbles stopped would have made a bad beer. And if I bottled it and fermentation continued I would have had bottle bombs.

Going by bubbles does not work and could be unsafe.

 

[BrunDog]

Don't go by bubbles. Active fermentation is not the end of fermentation. Yeast continue to clean up by-products. My rule of thumb: 3 weeks for mid-weight ales.

 

[FunkedOut]

This may rattle some cages, but I submit in the spirit of discussion towards progress.

I have been fermenting in kegs for about a year now.
Completely sealed fermenters with no leaks.
Easy to draw a sample from.

I use a cheap, homemade spunding valve with a large 0-30psi guage on it, with hash marks every 0.5 pounds.
I use a “precision” hydrometer with markings every 0.001 gravity points.
I ferment beer in a well insulated chest freezer with temp control, to within +/- 1*F in a thermowell at the center of the beer mass.

In my limited experience, towards the end of fermentation, I can measure an increase in pressure on the guage from day to day, without being able to measure a difference in SG.
This could mean that my instrument for measuring gravity is not as precise as my instrument for measuring pressure?
This could mean that the yeast are metabolizing compounds in the beer near the end of fermentation that are not affecting gravity, once all the sugars are gone?

I have gone 3-4 days observing slight pressure increases while measuring steady gravity readings, time after time.

I have concluded that the gravity readings are not as effective in determining active fermentation completion as the pressure readings. So much so, that I have stopped taking gravity readings to determine when to cold crash completely, and rely solely on the pressure guage.

Granted, just as there is a level of activity beyond what I can measure with my hydrometer, there has to be a level of activity beyond what I can measure with my pressure guage.
I always give my beer 2-3 days post completion before cold crashing.

Worst case, if I’m wrong on all this, I’ve been adding 1-4 days to to beer’s time on the yeast cake. Not a problem for my purposes.


Back to the OP, I would think that an airlock would be more sensitive to offgassing than building pressure on a guage.
This method should prove viable for determining the end of fermentation, in my opinion. Of course, this assumes no leaks, constant temperature and constant ambient pressure.
For automation, something like no bubbles + 3 days should work.

 

[S-Met]

have been fermenting in kegs for about a year now.
Completely sealed fermenters with no leaks.
Easy to draw a sample from.

I use a cheap, homemade spunding valve

Spunding/sealed vessel fermentation is a whole different discussion, probably beyond the experience of OP.

If you know your SG and maintain constant temperature and pressure as well as spunding gas into a secondary sealed container. In-line anomometer (more accurate) or psi gauge can be used to calculate volume of gas produced during fermentation. You can then calculate estimated abv using the Ideal Gas Law PV=nRT.

 

[Qhrumphf]

All an airlock bubbling means is the pressure inside the container is higher than the pressure outside.

More than fermentation or temp changes or a leaky bucket. Simply jostling the fermenter, as little as walking by it, can knock CO2 out of solution and increase the head pressure enough to bubble an airlock.

Dry hopping, or anything that forms nucleation sites, creates a LOT of bubbling.

As said, different liquid volumes in the airlock add their own pressure to it and will slow or speed the rate (the further below the surface, the more pressure it needs to overcome and the less it will bubble).

I routinely see no activity in a blowoff and still register dropping gravity at the tail end of fermentation, and that is in otherwise sealed conical fermenters. Because it's not generating enough pressure to overcome the pressure of the blowoff liquid.

If there was an easy way to automate it, especially something feasible/affordable to do at home, it would be all over the professional brewing world. And yet it's still daily gravity checks.

 

[crane]

Don't go by bubbles. Active fermentation is not the end of fermentation. Yeast continue to clean up by-products. My rule of thumb: 3 weeks for mid-weight ales.

+1

Since the OP is hell bent on counting bubbles, I would use the bubble rate to tell you when fermentation has peaked and starting to slow down. At this point I would raise the temperature for a diacetyl rest and wait another 3 to 5 days for clean up. This assumes that you are pitching a proper amount of healthy yeast into aerated/oxygenated wort.

My personal experience from trying to use a DIY bubble counter was that my old house shook too much when anyone walked through the room that it would produce bubbles for weeks after fermentation was complete.

 

[kh54s10]

I had a neglected beer sitting for almost a year. in month 10 or 11. It bubbled during a cold front. Bubbles tell you very little.

My most recent beer had stopped bubbling on day 3. On day 10 I took a hydrometer reading and dry hopped. On day 15 I took a reading and the gravity had dropped another .003 So by the bubble +3 days I would have gotten a very sweet beer. Or worse = bottle bombs.

 

[crane]

I had a neglected beer sitting for almost a year. in month 10 or 11. It bubbled during a cold front. Bubbles tell you very little.

My most recent beer had stopped bubbling on day 3. On day 10 I took a hydrometer reading and dry hopped. On day 15 I took a reading and the gravity had dropped another .003 So by the bubble +3 days I would have gotten a very sweet beer. Or worse = bottle bombs.

Sounds like you aren't using a hard walled fermenter (bucket) or have a leak. If yeast is actively fermenting it is producing CO2. The question in your case is where is it going? For it to stay inside the fermenter it would have to stay in solution and the volumes of CO2 in solution is easy to calculate with beer temp and headspace pressure. Since we have an airlock the pressure isn't changing. The beer could only have an increase in capacity of soluable CO2 if the temperature decreased during fermentation keeping the newly created CO2 in solution as it forms which would prevent the headspace pressure from increasing enough to create a bubble.

What I am describing is for someone who pitches a proper amount of healthy yeast into well aerated/oxygenated wort and has an effective means for controlling fermentation temperature. My ferments are predictably consistent with each type of yeast I use. YMMV.

I also raise temperatures as fermentation slows down to promote yeast activity during the final stages of fermentation and clean up. When you do this you will drive off more CO2 because of the whole boyle's law thing again. This creates more bubbles that aren't actually a sign of active fermentation. Ultimately you should always check your gravity at the end to make sure you hit your target FG. This would prevent you from kegging an unfinished ferment, but the wait x number of days is a good point to target when to take your first potential FG reading.

Again what I am describing is using it as a way to gauge when fermentation is starting to slow down, which is pretty consistent and predictable for me.

 

[MaxStout]

As others have noted, airlock bubbles (or lack thereof) are not a reliable indicator of the status of fermentation. Too many variables at play. It would be nice if there was some "shortcut" in which we could easily infer end of fermentation that way, but there isn't. Brewing, even at the hobbyist level, has a few complexities. One of those is the need to take accurate hydrometer readings and do so over a few days to determine if there is still a downward trend in gravity. Those of us who bottle--myself included--are acutely aware of the risk, as we don't want unfinished beer going into the bottles with priming sugar, creating bottle bombs.

Beer is serious business. Let's do it right!

 

[kh54s10]

I had a neglected beer sitting for almost a year. in month 10 or 11. It bubbled during a cold front. Bubbles tell you very little.

My most recent beer had stopped bubbling on day 3. On day 10 I took a hydrometer reading and dry hopped. On day 15 I took a reading and the gravity had dropped another .003 So by the bubble +3 days I would have gotten a very sweet beer. Or worse = bottle bombs.

Sounds like you aren't using a hard walled fermenter (bucket) or have a leak. If yeast is actively fermenting it is producing CO2. The question in your case is where is it going? For it to stay inside the fermenter it would have to stay in solution and the volumes of CO2 in solution is easy to calculate with beer temp and headspace pressure. Since we have an airlock the pressure isn't changing. The beer could only have an increase in capacity of soluable CO2 if the temperature decreased during fermentation keeping the newly created CO2 in solution as it forms which would prevent the headspace pressure from increasing enough to create a bubble.

What I am describing is for someone who pitches a proper amount of healthy yeast into well aerated/oxygenated wort and has an effective means for controlling fermentation temperature. My ferments are predictably consistent with each type of yeast I use. YMMV.

I also raise temperatures as fermentation slows down to promote yeast activity during the final stages of fermentation and clean up. When you do this you will drive off more CO2 because of the whole boyle's law thing again. This creates more bubbles that aren't actually a sign of active fermentation. Ultimately you should always check your gravity at the end to make sure you hit your target FG. This would prevent you from kegging an unfinished ferment, but the wait x number of days is a good point to target when to take your first potential FG reading.

Again what I am describing is using it as a way to gauge when fermentation is starting to slow down, which is pretty consistent and predictable for me.

I use Better Bottles with a stopper, so no there is no leakage. All this long reply only supports what I said. Bubbles tell you it is fermenting, lack of bubbles only tells you that co2 production is no longer exceeding the capacity of the fermenter to hold it in. But atmospheric and temperature changes can make a finished beer still in the fermenter bubble the airlock, even months later.

 

[crane]

I use Better Bottles with a stopper, so no there is no leakage. All this long reply only supports what I said. Bubbles tell you it is fermenting, lack of bubbles only tells you that co2 production is no longer exceeding the capacity of the fermenter to hold it in. But atmospheric and temperature changes can make a finished beer still in the fermenter bubble the airlock, even months later.

My point us that your example of bubbling stopping on day 3 but still seeing gravity dropping at day 10 goes against physics, unless the volume of your container is changing or you have a leak. Yeast cannot consume enough sugar to produce a measurable gravity drop without giving off CO2.

Also from my practical experience using a bubble counter that I made, you can use it to gauge when fermentation is slowing down and thus when you should raise for a diacetyl rest. It is too unreliable to be used for anything else.

 

[Qhrumphf]

My point us that your example of bubbling stopping on day 3 but still seeing gravity dropping at day 10 goes against physics, unless the volume of your container is changing or you have a leak. Yeast cannot consume enough sugar to produce a measurable gravity drop without giving off CO2.

Also from my practical experience using a bubble counter that I made, you can use it to gauge when fermentation is slowing down and thus when you should raise for a diacetyl rest. It is too unreliable to be used for anything else.

It has to produce enough *pressure* to overcome the pressure of the airlock to bubble.

Example:

Slow ramp down in an old-school lager. The yeast are still slowly active, at the same time that the temp is dropping. CO2 is produced and gravity still drops, but the drop in temp and pressure keeps the CO2 in solution. Hell without a positive pressure source you may even get suckback rather than airlock bubbling.

If you condition cold (many commercial breweries do to facilitate faster yeast harvesting), it's the same thing gravity can drop without any pressure increase as the temp drop keeps the CO2 in solution.

 

[crane]

It has to produce enough *pressure* to overcome the pressure of the airlock to bubble.

Example:

Slow ramp down in an old-school lager. The yeast are still slowly active, at the same time that the temp is dropping. CO2 is produced and gravity still drops, but the drop in temp and pressure keeps the CO2 in solution. Hell without a positive pressure source you may even get suckback rather than airlock bubbling.

If you condition cold (many commercial breweries do to facilitate faster yeast harvesting), it's the same thing gravity can drop without any pressure increase as the temp drop keeps the CO2 in solution.

In the example he is describing, there was no temp drop, no leak, nor any bubbles, yet there was a measurable drop I gravity. Not possible by the laws of physics.

 

[kh54s10]

My point us that your example of bubbling stopping on day 3 but still seeing gravity dropping at day 10 goes against physics, unless the volume of your container is changing or you have a leak. Yeast cannot consume enough sugar to produce a measurable gravity drop without giving off CO2.

Also from my practical experience using a bubble counter that I made, you can use it to gauge when fermentation is slowing down and thus when you should raise for a diacetyl rest. It is too unreliable to be used for anything else.

That hasn't been my experience. The few times I have measured the gravity shortly after the bubbles stopped and then took another one a few days later, the gravity was lower but there was not enough fermentation to create enough co2 for bubbles. We are talking of only a couple gravity points. Maybe it was because of my opening to get the gravity reading.

 

[acidrain]

You mention a zero bubble rule. I've never heard of this rule. Where did you see this?
The rule I know is "no hydrometer change over three days".
Automated or not, lack of bubbles do not automatically mean fermentation is over.
Even if you're fermenting in an airtight container like a keg, you should have a sample port as part of your automation.
Hell, slight temperature changes will cause bubbles.

 

[NeverDie]

In the example he is describing, there was no temp drop, no leak, nor any bubbles, yet there was a measurable drop I gravity. Not possible by the laws of physics.

Yes, that's what was thinking as well. I wasn't sure though whether the conversion of one kind of alcohol into another by the yeast toward the end of fermentation would release any gas, even if it might change SG. Anyone know?

Great discussion. I can see now that I had failed to consider changes in barometric pressure as a possible factor.

Anyway, I purchased a TILT, and, aside from the price, I'm very happy with it. I don't mind the price for one, but getting lots of them for many different brews in parallel could certainly add up. That's why I was hoping the bubble counter might be a proxy of some kind.

 

[augiedoggy]

I have been on the fence with buying a tilt for quite a while... also waiting for brucontrol to support it. Ive seen quite a few reports of it giving false reading and even gravity readings going backwards because of everything from krausen to bubbles on the glass surface being given as the cause.

 

[NeverDie]

I have been on the fence with buying a tilt for quite a while... also waiting for brucontrol to support it. Ive seen quite a few reports of it giving false reading and even gravity readings going backwards because of everything from krausen to bubbles on the glass surface being given as the cause.

It might (?), such as with a foamy yeast like Kveik. I haven't tried yet to confirm the readings to check for accuracy.