Mysterious, abrupt pressure fermentation halt

[BryskeBrynolf]

Howdy!

My first attempt at pressure fermentation. Got myself a Fermzilla 30L All Rounder with a spunding valve. Brewed a German(-ish) lager in the usual way. Pitched 2 packs of 34/70 at 10 °C and let it ride with no pressure for the first 3 days. Set the spunding valve at 0.8 bar on day 4 and observed the pressure rise to the desired level over a few hours. Fermentation chugged along as predicted, pressure constant at 0.8 bar. Started ramping up the temp by 1 °C per day. On day 6 fermentation suddenly stopped dead and the pressure started dropping (as expected I guess, since CO2 production ceased).

I had expected the fermentation to slowly subside towards some FG as it normally does, but here, it seems the yeasties were suddenly all obliterated. Does anyone with (or without) experience of pressure fermentation have any idea what happened?

 

[Broken Crow]

and the pressure started dropping

I do not have experience with pressure fermenting (yet, which is why I read about it here), But; especially given that you're ramping up the temp, the pressure should not be dropping. Sounds like you have a slow gas-leak.

 

[BryskeBrynolf]

Well, I reckon the beer gradually absorbs CO2 and if no new CO2 is added, the pressure drops (to the point of equilibrium). At least that's how it behaves in my kegs.

 

[hotbeer]

6 days, most if not all of your fermentation is probably finished. If you didn't get the pressures you expected, then perhaps you have a leak.

I don't pressure ferment. Since I got my raptPill, I've seen most all my ferments drop the SG rapidly to the FG or within a few points of the FG in about 2 to 4 days. Sometimes takes 4 or 5 days to eek out that last point of specific gravity.

Your current FG seems to be 1.010. So what are you concerned about?

Just because it's finished fermenting doesn't mean it's time to move it to keg or bottles. I'd wait till it's clear so that all the odd ball flavor and aroma notes are taken care of by the yeast. Also makes for less sediment on the bottom of the bottle.

 

[Mr. Vern]

Just stopping in to say I like your Avatar... Don Martin / Sergio Aragones are some of my favorites. You guys seem to have the pressure figured out.

 

[BryskeBrynolf]

6 days, most if not all of your fermentation is probably finished. If you didn't get the pressures you expected, then perhaps you have a leak.

I don't pressure ferment. Since I got my raptPill, I've seen most all my ferments drop the SG rapidly to the FG or within a few points of the FG in about 2 to 4 days. Sometimes takes 4 or 5 days to eek out that last point of specific gravity.

Your current FG seems to be 1.010. So what are you concerned about?

"Concerned" is too strong a word. I can live with 1.010 as FG. I'm wondering about the sudden and definitive halt of the fermentation. I'm regulary recording my fermentations with my TILT and I have never seen a curve like that. Two more days now and still bang at 1.010.

 

[mac_1103]

I reckon the beer gradually absorbs CO2

CO2 is more soluble in water at lower temperatures. Therefore, the beer will gradually lose CO2 as you increase the temperature.*

I have never seen a curve like that.

Really? Doesn't it have to flat-line eventually?

*edit - even at a constant temperature, the beer will only absorb CO2 if the pressure in the headspace is maintained

 

[BryskeBrynolf]

Really? Doesn't it have to flat-line eventually?

Yes of course. But gradually (asymptotically). Not abruptly like this.

Granted, my experience with 34/70 is limited. Maybe it is known for behaving wierdly?

 

[mac_1103]

Yes of course. But gradually (asymptotically). Not abruptly like this.

I'm still not sure what you mean. Your curve looks pretty asymptotic to me. The smoothness or (lack thereof) of the curve depends on the resolution that the data allows. The fact that you may be used to slower fermentations (and therefore better time resolution) doesn't mean that there's anything wonky about this particular fermentation.

edit - i.e., stretch out the x axis and the curve will look more asymptotic; compress the x axis and it will look even more abrupt.

 

[BryskeBrynolf]

I'm still not sure what you mean. Your curve looks pretty asymptotic to me. The smoothness or (lack thereof) of the curve depends on the resolution that the data allows. The fact that you may be used to slower fermentations (and therefore better time resolution) doesn't mean that there's anything wonky about this particular fermentation.

edit - i.e., stretch out the x axis and the curve will look more asymptotic; compress the x axis and it will look even more abrupt.

OK. Maybe I'm reading too much into the data. I'm eager to understand possible effects of pressure fermentation but this is probably unrelated to that, then.

I do, however have questions about the usefulness of pressure fermentation if the pressure drops to less than 0.1 bar after the fermentation is finished. I don't think I have any leaks. There is still some pressure in the Fermzilla, but nowhere near the set 0.8 bar.

 

[mac_1103]

I don't think I have any leaks.

I think you must. Or your spunding valve isn't working.

 

[BryskeBrynolf]

I think you must. Or your spunding valve isn't working.

Another interesting discussion.

With forced carbonation in kegs (as I normally do), you can't just crank the pressure up to the desired level for a couple of days, turn it off and be done with it. You have to continually add gas for many days to reach equilibrium at the target pressure. I imagine the same applies for pressure fermentation.

 

[hotbeer]

I'd think all the CO2 that is going to dissolve will be absorbed almost as quick as it's created. And with your temperature going up, then it should be coming out of solution. So if there isn't any pressure, there must be a leak. If your temperatures are going up and down, then that will cause the gas in the headspace to expand and contract. Which also has to be a consideration as the spunding valve will let gas out as it expands and if fermentation is over, then there won't be anything to replace it except for the limited amount of CO2 that comes out of solution as temp increases and/or pressure goes down.

So your experience with how it dissolves when added to a keg isn't quite the same as what is going on in the FV.

 

[mac_1103]

You have to continually add gas for many days to reach equilibrium at the target pressure.

Because you are starting with beer with very little dissolved CO2 and trying to increase the amount of dissolved CO2 significantly. You aren't doing that here. If anything, increasing the temperature should force more CO2 out of the beer.

There was a thread a few months back that started with a question similar to yours. I'm no expert on pressure fermentation but I'm pretty sure that the only reason for the pressure to drop more than a couple of PSI is gas leaking out somewhere (unless you are cold crashing).

 

[doug293cz]

Well, I reckon the beer gradually absorbs CO2 and if no new CO2 is added, the pressure drops (to the point of equilibrium). At least that's how it behaves in my kegs.

Another interesting discussion.

With forced carbonation in kegs (as I normally do), you can't just crank the pressure up to the desired level for a couple of days, turn it off and be done with it. You have to continually add gas for many days to reach equilibrium at the target pressure. I imagine the same applies for pressure fermentation.

I'd think all the CO2 that is going to dissolve will be absorbed almost as quick as it's created. And with your temperature going up, then it should be coming out of solution. So if there isn't any pressure, there must be a leak. If your temperatures are going up and down, then that will cause the gas in the headspace to expand and contract. Which also has to be a consideration as the spunding valve will let gas out as it expands and if fermentation is over, then there won't be anything to replace it except for the limited amount of CO2 that comes out of solution as temp increases and/or pressure goes down.

So your experience with how it dissolves when added to a keg isn't quite the same as what is going on in the FV.

Because you are starting with beer with very little dissolved CO2 and trying to increase the amount of dissolved CO2 significantly. You aren't doing that here. If anything, increasing the temperature should force more CO2 out of the beer.

There was a thread a few months back that started with a question similar to yours. I'm no expert on pressure fermentation but I'm pretty sure that the only reason for the pressure to drop more than a couple of PSI is gas leaking out somewhere (unless you are cold crashing).

@hotbeer almost has it right. The difference is this: the CO2 is created a molecule at a time, and is in solution as soon as it is created. It only coalesces into bubbles when the concentration of CO2 in the beer is higher than the equilibrium concentration at the current beer temperature, and the current headspace CO2 partial pressure. The headspace starts out at ~0 CO2 partial pressure, but the headspace CO2 partial pressure very quickly increases once fermentation gets underway (either to 14.7 psi/1 bar or the spunding pressure +14.7psi/1 bar.) Once CO2 starts coming out of the beer, the beer is saturated with CO2, and will not retain/absorb any more unless the temperature is reduced, or the headspace CO2 partial pressure is changed. Decreasing CO2 partial pressures causes reduced CO2 retention in the beer, and increased CO2 partial pressure causes increased retention or absorption from the headspace.

So, if pressure starts dropping once it has increased, you have a leak issue.

@mac_1103 touches on the difference between what's happening in fermentation caused carbonation, and post fermentation forced carbonation. In forced carbonation, the headspace CO2 partial pressure starts out much higher than the equilibrium partial pressure for the starting carb level of the beer, so the beer slowly absorbs CO2 from the headspace. If the CO2 in the headspace is not replaced (CO2 source remains connected) as it is absorbed, the headspace pressure will drop, and at some point equilibrium will be reached and absorption of CO2 by the beer will cease at a level much lower than what the initial CO2 pressure would provide.

Brew on

 

[BryskeBrynolf]

Very interesting. Thanks for the initiated analyses and references.

I will burp some artificial CO2 into the vessel tomorrow and see what happens. Or maybe rather when the vessel is empty, to rule out any other parameters than leakage.

 

[DuncB]

You may just have your spunding valve set too low.
When the ferment is active a lot of gas is being produced. When the gas production is well in excess of your setting the pressure will rise and stabilise. In your case at 0.8 bar.
When the ferment finished gas loss through the spund valve was greater than production and so pressure fell.
It is possible that the spund valve has a leak, my first metal valve had a crack in the brass T which coped during active ferment. But once ferment finished last all pressure. Took me several exasperating brews to find this.
What I would do is take the spund valve off. It's likely that some gas will still be made. Check with another gauge in a few hours if it's risen the spund is your source of loss.
If no rise then inject gas and check for leaks around lid, posts etc.

That high temp was an aberrant reading on day 5.
This was under spund from day 2 and risen slowly to 26 psi at 21 C.
With 21 litres of beer and 14 litres of headspace this should be around 2.4 vols and will be around this region once cold crashed and fined.
Hope this helps.
Video in top corner is listening to the cricket commentary.

 

[BryskeBrynolf]

Thanks. As if regular brewing wasn't complicated enough...

 

[doug293cz]

Luckily, we don't have to understand all of the physical chemistry, organic chemistry, and bio-chemistry in order to make beer.

Brew on

 

[mac_1103]

CO2 is created a molecule at a time, and is in solution as soon as it is created

Have you seen this @doug293cz? Not really sure what to make of it since they don't address how the CO2 is getting out of the cells (except by speculating).

 

[doug293cz]

Have you seen this @doug293cz? Not really sure what to make of it since they don't address how the CO2 is getting out of the cells (except by speculating).

Interesting. Don't have time to read and digest it right now.

Brew on

 

[Rikk]

I pressure ferment and use a tilt. From what I see you are done fermentation. Simple as that. You should not be losing pressure unless you 1) have a leak or 2) are cold crashing.

 

[DuncB]

Did you discover if the fermzilla was leaking or a setting on the spunding valve?

 

[mashdar]

Have you seen this @doug293cz? Not really sure what to make of it since they don't address how the CO2 is getting out of the cells (except by speculating).

I'm not sure if "secreted" means via diffusion? Or direct bubble expression?

I wonder if intracellular bubbles can affect cell buoyancy.

 

[doug293cz]

I'm not sure if "secreted" means via diffusion? Or direct bubble expression?

I wonder if intracellular bubbles can affect cell boutancy.

I find it hard to believe that a stable sized bubble could pass thru a cell wall. It seems much more plausible that CO2 would diffuse thru the cell wall, in which case it would be in solution when it exited the yeast cell.

Bubbles need to be a minimum size to be thermodynamically stable. When a gas is supersaturated in solution, it wants to reduce the total free energy by coming out of solution. It can do that by exiting the solution at the liquid/gas interface, or forming a bubble. But forming a bubble requires energy in itself, because a new liquid/gas interface has to be created, and the surface tension of the bubble increases the pressure in the bubble above the equilibrium pressure for the gas in solution. The smaller the bubble, the higher the pressure inside the bubble. If the pressure in the bubble is higher than what would be the equilibrium pressure for the gas at its current concentration in solution, the bubble is unstable and may collapse, unless it quickly grows larger, and reduces the internal pressure to become stable.

Brew on

 

[mac_1103]

I find it hard to believe that a stable sized bubble could pass thru a cell wall.

It would have to be something akin to exocytosis.