Open Fermentation and/or Different Fermenter Geometry.

Twostage said:

I get the space efficiency and depending on material it would also be easier to make rectangular than round but I'm thinking about the affect of the shape on how fermentation proceeds and therefore, ultimately, flavour.

Can't remember if it was the Kolsch or Altbier book I've read recently but there was a definite preference for long and low rather than narrow and tall. There was an understanding that shallow worked better for them than deep. Other breweries choose tall (enormous) cylindrical fermenters. So depth impacts, but that isn't shape.

During vigorous fermentation there are convection currents which will be influenced by shape. There may be other things going on too which are dictated by having corners .

Going to have to get one of those food serving things and do a test.

Going to watch the Sierra N. video too .

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The most cost-effective fermenters are round, only one seam to weld. It would be interesting to know the relationship between depth and surface area. though, I suspect it wouldn't really matter on a homebrew scale.

Mr & Mrs Smith said:

It would be interesting to know the relationship between depth and surface area. I suspect it wouldn't really matter on a homebrew scale.

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It can. See post #11 Edsbeerblog and the tweet from Prof. Dawn Maskell, yeast physiologist and Director of the International Centre for Brewing and Distilling at Heriot-Watt University.

I brewed a Düsseldorf Altbier this morning which I'm fermenting open - early days yet but I'm expecting a much bigger krausen than this in the next 24-48hrs

Sadfield said:

Most of the time once there's sign that the krausen is about to drop, rack the beer into a purged corny keg via a tap on the bottom of the FV. Letting it ferment out. Occasionally, I'll just put the stainless lid on.

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Just checking again on this point @Sadfield - how many SG points away from FG would you estimate the beer is when you transfer it from open fermentation to keg?

I had been reckoning on 1 day in primary per °P starting gravity, i.e. 11 days for an 11°P wort (rule of thumb from Czech Pilsner brewing but I think I'm being daft and confusing myself).

But I'm sure an ale krausen would have dropped long before this (3-5 days after pitching maybe???) so I'd have to close up the FV for a few days before transferring. And by 11 days it's probably done fermenting so not enough left to carbonate in the keg.

So I'm thinking the whole "1 day in primary per °P starting gravity" is off the mark, for ales at least. Maybe 0.5 days / °P is more like it???

matt76 said:

Just checking again on this point @Sadfield - how many SG points away from FG would you estimate the beer is when you transfer it from open fermentation to keg?

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What like about the process is it is very sensory, when it looks like it's slowing down, I'll drop it. Typically on the third day after pitching. When I have taken gravity readings before transfer it's usually around 3-5 points away.

Stainless steel sinks make great open fermenters. Seem to be cheap as at our local recycling centre. Conveniently they have a drain hole in the bottom.

Sadfield said:

It can. See post #11 Edsbeerblog and the tweet from Prof. Dawn Maskell, yeast physiologist and Director of the International Centre for Brewing and Distilling at Heriot-Watt University.

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The relationship I had in mind was surface area to depth if there was an equation, but reading what Briggs says there isn't. Just a depth of 2 to 4 meters despite surface area.

Twostage said:

. Other breweries choose tall (enormous) cylindrical fermenters. So depth impacts, but that isn't shape.
During vigorous fermentation there are convection currents which will be influenced by shape. There may be other things going on too which are dictated by having corners .

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The towers are very efficient fermenters, the paddles/propellors inside them keep the yeast and nutrients moving as well as stabilising temperature. As for hydrostatic pressure if there is a force pushing down (gravity) does the blades of the propellors pushing up neutralise somewhat the force of gravity?
Any engineers in fluid mechanics engineers on board?

Mr & Mrs Smith said:

The relationship I had in mind was surface area to depth if there was an equation, but reading what Briggs says there isn't. Just a depth of 2 to 4 meters despite surface area.

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In what regard? I can't see how there isn't a relationship between volume and surface area when it comes to off gassing of CO2, and the stripping of volatiles. Or, contact of wort to air.

Mr & Mrs Smith said:

Any engineers in fluid mechanics engineers on board?

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Yes, masters degree plus 25 years continuous professional experience

Mr & Mrs Smith said:

As for hydrostatic pressure if there is a force pushing down (gravity) does the blades of the propellors pushing up neutralise somewhat the force of gravity?

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No. The propellers or stirrers have no significant effect on the pressure in the tank.

The yeast will experience a pressure equal to "static pressure" + "hydrostatic pressure"

If the tank is open then static pressure will be atmospheric pressure (1atm).

If they're closed and fermenting under pressure then it will be atmospheric pressure plus whatever the spunding valve is set to - I would guess about 15psi or 1bar or 1atm, making it something like 2atm static pressure.

Now we add on hydrostatic pressure which is density x gravity x depth. At the surface the depth is zero so hydrostatic pressure is also zero. But in a 10m tall tank hydrostatic pressure at the bottom would be about 1atm.

So, adding together both the static and hydrostatic pressure components, in a 10m tall pressurised FV it's plausible the yeast at the bottom are experiencing a total of 3atm pressure, the same as you would experience scuba diving at a depth of 20m - all this for an organism that, like you and me, has evolved to live in 1atm.

Now what Prof. Maskell says in her tweet is that according to her research, depths less than many metres can have an impact on yeast. But what she doesn't say is when is depth no longer significant, e.g. mm, cm, 10's of cm, m.

https://coloradobeer.org/tech-safety-posts/yeast-storage/#:~:text=Hydrostatic pressure from all the,with increasing pressure and time.

Looking at this, if the hydrostatic pressure of c1.5m can kill yeast in time, then surely depths of much less can at the very least impact on performance when added to all other factors such as co2 and alcohol in the solution.

Sadfield said:

Typically on the third day after pitching. When I have taken gravity readings before transfer it's usually around 3-5 points away.

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Do you leave it open from pitching, or put some kind of cover on it while the yeast gets going? I'd be worried about creepy crawlies until the krausen formed.

this was my question earlier-open (no airlock) or open (covered with cloth) or open (nothing).

I am with you open (covered) is ok, but open open .. nah

I cover it with the lid whilst it gets going. I think if you are doing it in a clean fridge it'll be OK. It'd probably be OK any way if you pitch enough healthy yeast, people have been brewing this way for centuries. Also, flies are attracted by esters, its why yeast produces them. Hitching a ride on flies is how yeast dissipates in nature. Prior to fermentation there aren't any esters.

Sadfield said:

What like about the process is it is very sensory, when it looks like it's slowing down, I'll drop it. Typically on the third day after pitching. When I have taken gravity readings before transfer it's usually around 3-5 points away.

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One more question on the details of this transfer - presumably you leave behind any yeast cake (such as it is) on the bottom of the FV, but what about the krausen?

Presumably you want to transfer before the krausen has completely gone, otherwise there's a bigger risk of oxidation? But do you want to deliberately transfer the krausen or try to avoid it?

I'd guess try to avoid it as at that point maybe it's mainly dead yeast cells, but I could be wrong. And I'd imagine this early in fermentation there's still plenty of yeast left in suspension to finish the job so no need to hoover up the yeast cake or krausen.

Sadfield said:

I cover it with the lid whilst it gets going. I think if you are doing it in a clean fridge it'll be OK. It'd probably be OK any way if you pitch enough healthy yeast, people have been brewing this way for centuries. Also, flies are attracted by esters, its why yeast produces them. Hitching a ride on flies is how yeast dissipates in nature. Prior to fermentation there aren't any esters.

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Used to hitch a ride on a cross bar - gave that up too

I just rack the beer to the keg and the krausen joins the trub in the bottom of the FV.

matt76 said:

Yes, masters degree plus 25 years continuous professional experience

No. The propellers or stirrers have no significant effect on the pressure in the tank.

The yeast will experience a pressure equal to "static pressure" + "hydrostatic pressure"

If the tank is open then static pressure will be atmospheric pressure (1atm).

If they're closed and fermenting under pressure then it will be atmospheric pressure plus whatever the spunding valve is set to - I would guess about 15psi or 1bar or 1atm, making it something like 2atm static pressure.

Now we add on hydrostatic pressure which is density x gravity x depth. At the surface the depth is zero so hydrostatic pressure is also zero. But in a 10m tall tank hydrostatic pressure at the bottom would be about 1atm.

So, adding together both the static and hydrostatic pressure components, in a 10m tall pressurised FV it's plausible the yeast at the bottom are experiencing a total of 3atm pressure, the same as you would experience scuba diving at a depth of 20m - all this for an organism that, like you and me, has evolved to live in 1atm.

Now what Prof. Maskell says in her tweet is that according to her research, depths less than many metres can have an impact on yeast. But what she doesn't say is when is depth no longer significant, e.g. mm, cm, 10's of cm, m.

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Good stuff, I did some reading overnight, Brewing Yeast and Fermentation Chris Boulton and David Quain. It was an informative read the that chapters covered fermenting vessels made of animal skins through to modern-day conical cylindrical fermenters reaching 18 meters in height.
There are no concerns about hydrostatic pressure apart from the flocculating yeast, but the modern brewery has timers for the yeast drop from the cone. As we know the yeast from these large fermenters have a limited life before they are discarded. In contrast, open fermentation and yeast cropping from the top the practice can go on for years without mutation, as can continuous fermentation systems.
So hydrostatic pressure. The impact is the CO2 bubbles decrease the hydrostatic pressure plus carry the yeast back into suspension they will know where they are most comfortable, and it won't be at the bottom of a tall FV.
The CF Towers are interesting, able to fully attenuate an ale in 3-4 hours and a lager in 8-12 hours!
A book well worth having in the library.

Depth in the early days of brewing was a significant factor in the open fermenters. It was thought that anything over a meter was not desirable, that was in 1954 if I remember right, but that concept was short-lived Guinness open fermenter is 7 meters deep.
Another question that arises from what I have read is secondary fermentation vessels, who uses them? Something for a separate post.

Mr & Mrs Smith said:

Another question that arises from what I have read is secondary fermentation vessels, who uses them? Something for a separate post.

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The Germans with Kolsch and Altbeirs. I've a feeling a lot of (most ?) lagers as lagering is a really slow fermentation.

Plus every homebrewer in the 70s. It was the norm back then to rack into a secondary. My dad did it.

I've never done it but if I made a Kolsch or Alt I would.

Mr & Mrs Smith said:

Another question that arises from what I have read is secondary fermentation vessels, who uses them? Something for a separate post.

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My impression is that secondary is still common if not standard in commercial brewing (could be wrong though!) but no longer the norm in homebrewing as the risks outweigh any benefits.

I have an Altbier I'm fermenting open at the moment which I'll transfer to keg with a spunding valve once the krausen looks like it's dropping - never tried this before but I suppose this constitutes a transfer to secondary...

...but then it'll also be the serving vessel so who knows what it should be called!

Secondary isn't a vessel it's a maturation process. It can be done in the FV or a separate vessel. I see a lot of homebrewers confuse that and talk about package straight after hitting their FG.

There's a good discussion about it with John Palmer in the Brulab podcast #134.