[denny]

Attention, attention... this episode is brought to you by an accidentally awesome quirk of fate. After we announced our experiment (Saison Yeast - Airlock vs. Open Ferment - Does it prevent "stall") way back when, our itinerant "Science" co-host Marshall Schott let us know that his site, Brulosophy.com was running the same experiment!

We waited and coordinated our experimental results release. Marshall released his results earlier this week and now we get together and discuss our results plus his. There are a total of five experimental runs here and what do they say? Well, put yer earbuds in and listen! (And if you think this is the last time we're doing this.. ha, you don't know how all this works! Maybe we'll do it on purpose next time!)

From our time in the Casa Verde labs, we move back to Baltimore and spend some time with the Free State Homebrew Club Guild at HomeBrewCon's "Craft Beer Kickoff" Party. We had a heck of a time with the various club members and we hope you learn a thing or two! (Plus, hey - why do you homebrew?) So come along with as we talk to a raft of clubs and a beer "celeb" or two!

https://www.experimentalbrew.com/sites/default/files/ExperimentalBrewing_Episode_018_Saison_Under_Pressure.mp3

[brewinhard]

Very timely Denny as posted earlier.

I brewed up my saison with 3724 and am trying out the foil method instead of an airlock this time. Hoping to avoid the stall.

[charles1968]

Healthy well aerated starter means higher ergosterol level and no need for extra oxygen. Pitching without starter into wort under airlock means an oxygen sensitive yeast is O2 limited. Suggests it's about oxygen rather than pressure.

[denny]

Healthy well aerated starter means higher ergosterol level and no need for extra oxygen. Pitching without starter into wort under airlock means an oxygen sensitive yeast is O2 limited. Suggests it's about oxygen rather than pressure.

I think it's about CO2 toxicity as Jeremiah the chemist suggested.  And IIRC most people made starters.

[charles1968]

Healthy well aerated starter means higher ergosterol level and no need for extra oxygen. Pitching without starter into wort under airlock means an oxygen sensitive yeast is O2 limited. Suggests it's about oxygen rather than pressure.

I think it's about CO2 toxicity as Jeremiah the chemist suggested.  And IIRC most people made starters.

I'm not remotely convinced by the argument that an airlock can exert significant pressure. It's designed to release pressure. The only force exerted by the airlock on the beer is the weight of the water between the two different levels - a matter of a few grams! Compare that to the pressure in a bottle during bottle conditioning with Dupont - no problem there.

[charles1968]

Good podcast, by the way. Interesting discussion with Malcolm. I think his result was valid but if he repeats it, I'd skip the starter.

Airlock vs foil worth trying with British strains. Not many British homebrewers make beer under airlock - probably because traditional ale yeasts are prone to stalling. Some need rousing almost daily to finish the job.

[brewinhard]

FWIW, I have always used a healthy starter when brewing saison's with 3724, and have always experienced a stall between 1.020-1.030 even with healthy aeration and ramping of temps (up to low 80'sF) with an airlock.

I am still a little unsure about Marshall's validity for his version of the experiment since he was constantly taking off the airlock for many hydrometer samples. This could have been enough to "relieve" CO2 buildup (if that is what is going on) and keep the fermentation chugging away.

Either way, I do feel that Jeremiah's take on CO2 toxicity might have some value as well.

[69franx]

FWIW, I have always used a healthy starter when brewing saison's with 3724, and have always experienced a stall between 1.020-1.030 even with healthy aeration and ramping of temps (up to low 80'sF) with an airlock.

I am still a little unsure about Marshall's validity for his version of the experiment since he was constantly taking off the airlock for many hydrometer samples. This could have been enough to "relieve" CO2 buildup (if that is what is going on) and keep the fermentation chugging away.

Either way, I do feel that Jeremiah's take on CO2 toxicity might have some value as well.

This bit about regular readings alleviating pressure or co2 buildup was exactly what I thought as well. I have brewed 1x under airlock with 3724, and it went from 1.051 down to 1.009. Maybe a little high, but I never noticed it, it was very dry to me. Also tried Jon's 3724 and 3711 trick with a 1L starter just on the 3724 with only a foil covering, and again went from around 1.05 down to 1.005/6 IIRC, just as tasty as the first and I could not notice the difference in FG. I don't have a lot of experience with drinking commercial or homebrew saisons though

edit: the second batch with the combo of 3724 and 3711 actually finished at 1.003 from 1.050, so considerably lower, but I could not really taste the difference a year in between identicial recipes with just the yeast change and foil for covering

[charles1968]

Taking off the airlock equalizes pressure, but so does allowing the bubble to exit the airlock. The airlock only exerts pressure when the water levels on both sides are different. The pressure it creates is negligible:

P = density of water * g * h
where h is the height difference between the two ends if the blob of water.

P = 1000 * 10 * 0.02 = 200 Pa
1atm = 100,000 Pa so the change is 1/500 atm or 0.029psi.

Given that saison can bottle condition to maybe 20-30 psi, which is 1000 times greater, the idea that 0.029 psi would halt fermentation is daft.

However, an airlock is completely effective at stopping oxygen getting in. 

Calculation from a physicist friend.

[Todd H.]

I think it's about CO2 toxicity as Jeremiah the chemist suggested.  And IIRC most people made starters.
[/quote]

Just curious... how much more CO2 would be in the airlocked carboy?  As pointed out below, the difference in pressure is ~0.03 psi.  CO2 is heavier than air, so it's just sitting there under the foil, albeit slowly diffusing out from under the foil as enough is produced by fermentation to displace it.  The airlocked carboy likely always has a little bit more CO2 on top (well, 0.03 psi worth).  Does that really cause dissolved CO2 to be high enough in the airlocked carboy that the yeast suffer?  If so, damn they are sensitive.
I'd agree with Charles1968 below that O2 makes more sense, assuming enough O2 passively diffuses in and passively dissolves in the fermenting beer to make a difference.  Again, conjecture.
Just what makes sense to me (without data to back it up) as a former yeast biologist.  Who knows, I could be wrong.  Maybe that tiny amount of extra CO2 really does matter.  Or a combination of a little less CO2 and a little more O2?

[denny]

Good podcast, by the way. Interesting discussion with Malcolm. I think his result was valid but if he repeats it, I'd skip the starter.

Airlock vs foil worth trying with British strains. Not many British homebrewers make beer under airlock - probably because traditional ale yeasts are prone to stalling. Some need rousing almost daily to finish the job.

You seem to have missed a couple things...we all think it's more a case of CO2 toxicity rather than pressure.  And we were talking to Marshall, not Malcolm.  Sorry if we didn't make all that clear.

[charles1968]

And we were talking to Marshall, not Malcolm.  Sorry if we didn't make all that clear.

Yep, sorry - got the names mixed up.

we all think it's more a case of CO2 toxicity rather than pressure.

It still doesn't make sense though. If the pressure rise is negligible, the extra CO2 kept in solution by pressure will be negligible too. And bottle-conditioned saison still has a far higher level of CO2 than fermenting wort (hundreds of times higher?) yet it still attenuates out.

There's a plausible mechanism for oxygen because we know some yeast strains are O2 limited due to ergosterol needs. It's highly strain dependant. No plausible mechanism for CO2 toxicity has been put forward that I'm aware of.

Also I think it's interesting that many brewers make saison under airlocks and don't have problems. I suspect they're aerating well and using healthy starters. If you don't tick all the boxes, you're more likely stall.

Either way, the advice to use foil instead of an airlock is good.

[denny]

And we were talking to Marshall, not Malcolm.  Sorry if we didn't make all that clear.

It still doesn't make sense though. If the pressure rise is negligible, the extra CO2 kept in solution by pressure will be negligible too. And bottle-conditioned saison still has a far higher level of CO2 than fermenting wort (hundreds of times higher?) yet it still attenuates out.

There's a plausible mechanism for oxygen because we know some yeast strains are O2 limited due to ergosterol needs. It's highly strain dependant. No plausible mechanism for CO2 toxicity has been put forward that I'm aware of.

Also I think it's interesting that many brewers make saison under airlocks and don't have problems. I suspect they're aerating well and using healthy starters. If you don't tick all the boxes, you're more likely stall.

Either way, the advice to use foil instead of an airlock is good.

When you say that, though, you;re assuming you know how much CO2 is there and how much it takes to affect the yeast.  I don't think either of us has a handle on it.  And the experiment wouldn't have come about if a large number of brewers hadn't reported problems with this strain of yeast.  Of course people make saison without problems, but many of those are using a different yeast.  Stalls with the Dupont strain are very frequently reported.  And keep in mind that most of these batches did use a healthy starter and were well aerated.

[charles1968]

I know you can bottle condition with this yeast as I've done it, so I'm not sure CO2 is toxic to it. The fact that it stalls but continues attenuating very slowly suggests to me that some kind of limiting factor is at work.

[brewinhard]

My one question with using foil method instead of an airlock has to do with oxidation.

Has Drew (or anyone else using this extended foil method) experienced oxidation effects on malt/hops over long aging periods?  Any reason to think that a negative staling reaction might occur with allowable oxygen able to potentially ingress as fermentation slows?  Just thinking out loud.