Fermenter Stir Plate

[schooey]

I considered making the joke myself, but thought I'd try to keep the civility of this thread at a level at least equal to where it started.

Dude... no joke intended; I did say seriously... For $60 odd dollars it's a cheap enough experiment.

I was thinking if you put something like this in the fermenter for a high floccing yeast, but only activated it for short bursts (say 30 seconds every 4 hours) once the ferment was well underway (say 60+ hours) and CO2 production was highly active, would it really be any danger of oxidating the beer?

TB: I make all my starters with an airlock fitted to the flask, but I use a 20 second shot of O2 with an 0.5u airstone before pitching the yeast, and another 10 second shot at 6 hours. I haven't noticed any issues with the starters and they are usually at high krausen by 12-18 hours. Is this not a good practice?

 

[TidalPete]

Paul Sorrenson had it all sorted years ago. LINKY

TP

 

[Thirsty Boy]

I considered making the joke myself, but thought I'd try to keep the civility of this thread at a level at least equal to where it started.


This is the argument I get each time I discuss the topic - and it's come to argument - but I'm yet to be convinced that even a good vortex is pulling in a significant amount of oxygen through the neck of a conical flask sealed loosely with foil. If that WERE true, then surely I could test it by simply replacing the foil with some sort of device that indicates the direction of pressure... say, an S-bend airlock, perhaps.

Strangely, when I attach my airlock to each of my starters, I invariably get bubbling, even at the start of yeast production. Go figure.

I have more trouble believing that against the net pressure (or even, for arguments sake, in the case of zero net pressure) diffusion past loosely scrunched foil is leading to a viable source of oxygen, as opposed to a lowered partial pressure of oxygen in the flask, but that said I'll gladly accept good scientific evidence to the contrary.

Fair enough... But nobody said anything about a vortex pulling oxygen in. The stir plate simply breaks up the surface tension a bit and increases the surface area, which allows the oxygen to dissolve into the liquid a bit better. Even if there is no "extra" oxygen getting into the flask, it enables the oxygen that's in there already to more easily get into the wort as the yeast reduce the level of oxygen that's already dissolved.

The whole thrust of my argument, and I thought it was quite clear, was that there is a period, where there is no positive pressure, when the oxygen is able to cross the loose barrier of a piece of foil... And that after there is positive pressure, it obviously can't.

You obviously dont believe this to be the case because you get bubbling through your airlock as soon as you pitch your yeast into your starter... I never did, and I can think of nothing that I have learned about yeast that would cause co2 evolution very early in the process... If it is evolving co2, then its already past the point where it particularly needs the oxygen. I could see it happening if you pitch a smacked yeast pack, as of course the stir plate will knock the co2 out that's dissolved in the liquid in the pack, but after that, things should just sit still while the yeast sucks in the O2 for a while. Thats what happens when I make a starter.

At any rate, I don't particularly have to provide a compelling scientific argument from my point of view. I have given an arm waving but reasonably sound argument, and it is supported by the understanding and practice of many experienced home brewers, the suggested methods of yeast propagation in the brewing text books, the practice of yeast propagation departments in breweries all around the world and the practice in yeast propagation labs all around the world.

If you think you know better, well and good - perhaps you do - but I suggest that the onus is on you to do the research and come up with good scientific reasons why you are right and everyone else is wrong, rather than visa versa.

TB: I make all my starters with an airlock fitted to the flask, but I use a 20 second shot of O2 with an 0.5u airstone before pitching the yeast, and another 10 second shot at 6 hours. I haven't noticed any issues with the starters and they are usually at high krausen by 12-18 hours. Is this not a good practice?

With the extra shots of 02 I doubt it would make much difference in your case, but studies i have read find that you get better growth from a stir plate starter with a porous closure than you do from a non porous one like an airlock. But, if as QB suggests, i am wrong about the oxygen stuff... Then it may well have to do with increased pressure of C02 in an "air locked" vessel and thus higher dissolved CO2 & nothing to do with oxygen at all.

It's not bad practice to airlock your starter - it just that you might well find that you get better growth from an non-airlocked one. Although, as i said, with your O2 at start and 6 hrs... It might not make a he'll of a lot of difference at all.

 

[jonocarroll]

Sorry thread for the slight OT, but this IS relevant to anyone looking here for stirplate science... (if anyone's going to delete this, please ask first, it took a while).

At any rate, I don't particularly have to provide a compelling scientific argument from my point of view. I have given an arm waving but reasonably sound argument, and it is supported by the understanding and practice of many experienced home brewers, the suggested methods of yeast propagation in the brewing text books, the practice of yeast propagation departments in breweries all around the world and the practice in yeast propagation labs all around the world.

If you think you know better, well and good - perhaps you do - but I suggest that the onus is on you to do the research and come up with good scientific reasons why you are right and everyone else is wrong, rather than visa versa.

Funny how fast a scientific discussion turns to defensive reasoning and sooky-la-las. Well, if "everyone" "knows" that I'm "barking up the wrong tree" then I may as well pack it in and accept your argument. No reason to question such cut and dry proof. </sarcasm>

If you think you know better, well and good - perhaps you do - but I suggest that the onus is on you to do the research and come up with good scientific reasons why you are right and everyone else is wrong, rather than visa versa.

Okay then. Point taken. I had assumed by the fact that you argued against my point (argued in the debate sense, not taking it personally) that you had some sort of evidence to the contrary that you were relying on. Perhaps not, let's do some research shall we? Let's start here:

You obviously dont believe this to be the case because you get bubbling through your airlock as soon as you pitch your yeast into your starter... I never did, and I can think of nothing that I have learned about yeast that would cause co2 evolution very early in the process...

Let's look at the metabolic pathway for yeast;



Glucose is converted to pyruvate, then one of two things happen. When no oxygen is present the pyruvate is decarboxylated into acetaldehyde -- releasing the familiar CO₂ -- which is then reduced to ethanol. Nothing wrong there, but when oxygen IS present, the pyruvate enters the Krebs cycle (citric acid cycle) which, sure enough, produces CO₂ via decarboxylation.

[Edit: Just checked - aren't you studying this? Shouldn't you know this?]

So, CO₂ is produced in the aerobic phase. This will be evolved out of solution creating a net flow of gas out of the starter. I'm not saying that's enough to completely stop the diffusion of oxygen into the flask (actual velocity of oxygen molecules at room temperature >>> group velocity of outgoing CO₂, granted) but I think this is going to be a very small fraction compared to the amount of dissolved oxygen in a well aerated starter.

[ Some references so far;
'Brewing - Science and Practice' (Briggs et al., 2004) -- a brewing text book if ever there was one,
'Beer - tap into the art and science of brewing' (Bamforth, 2003),
'Alcoholic Fermentation in Yeast Investigation' (Doherty & Waldron, 2009),
http://en.wikipedia.org/wiki/Krebs_cycle ]

I'm a little tired of this just this minute, but I'll see if I can actually find any references to a stir place *scientifically* assisting more than keeping the yeast in suspension. All I managed to find searching (refer above - I do know how to search) seems to fail to mention anything further. I get the feeling that there's a lot of similarity to the tale I heard on here a while ago...

Bob: Why do you cut the bone off the roast?
Alice: I dunno, mum always did it.
Alice: Mum, why did you cut the bone off the roast?
Mum: I dunno, my mum always did it.
Alice: Grandma, why did you cut the bone off the roast?
Grams: It didn't fit in the pan.

except it usually ends up that someone comes up with a pseudo-scientific argument for X (e.g. cutting off the bone) that makes enough sense that everyone blindly uses said argument to justify X in the future. Does snopes.com have an entry on stirplates? Meh.

 

[proudscum]

Sorry thread for the slight OT, but this IS relevant to anyone looking here for stirplate science... (if anyone's going to delete this, please ask first, it took a while).


Funny how fast a scientific discussion turns to defensive reasoning and sooky-la-las. Well, if "everyone" "knows" that I'm "barking up the wrong tree" then I may as well pack it in and accept your argument. No reason to question such cut and dry proof. </sarcasm>


Okay then. Point taken. I had assumed by the fact that you argued against my point (argued in the debate sense, not taking it personally) that you had some sort of evidence to the contrary that you were relying on. Perhaps not, let's do some research shall we? Let's start here:


Let's look at the metabolic pathway for yeast;

View attachment 42536

Glucose is converted to pyruvate, then one of two things happen. When no oxygen is present the pyruvate is decarboxylated into acetaldehyde -- releasing the familiar CO₂ -- which is then reduced to ethanol. Nothing wrong there, but when oxygen IS present, the pyruvate enters the Krebs cycle (citric acid cycle) which, sure enough, produces CO₂ via decarboxylation.

[Edit: Just checked - aren't you studying this? Shouldn't you know this?]

So, CO₂ is produced in the aerobic phase. This will be evolved out of solution creating a net flow of gas out of the starter. I'm not saying that's enough to completely stop the diffusion of oxygen into the flask (actual velocity of oxygen molecules at room temperature >>> group velocity of outgoing CO₂, granted) but I think this is going to be a very small fraction compared to the amount of dissolved oxygen in a well aerated starter.

[ Some references so far;
'Brewing - Science and Practice' (Briggs et al., 2004) -- a brewing text book if ever there was one,
'Beer - tap into the art and science of brewing' (Bamforth, 2003),
'Alcoholic Fermentation in Yeast Investigation' (Doherty & Waldron, 2009),
http://en.wikipedia.org/wiki/Krebs_cycle ]

I'm a little tired of this just this minute, but I'll see if I can actually find any references to a stir place *scientifically* assisting more than keeping the yeast in suspension. All I managed to find searching (refer above - I do know how to search) seems to fail to mention anything further. I get the feeling that there's a lot of similarity to the tale I heard on here a while ago...

Bob: Why do you cut the bone off the roast?
Alice: I dunno, mum always did it.
Alice: Mum, why did you cut the bone off the roast?
Mum: I dunno, my mum always did it.
Alice: Grandma, why did you cut the bone off the roast?
Grams: It didn't fit in the pan.

except it usually ends up that someone comes up with a pseudo-scientific argument for X (e.g. cutting off the bone) that makes enough sense that everyone blindly uses said argument to justify X in the future. Does snopes.com have an entry on stirplates? Meh.

glad i dropped the little "only if you really like oxidised beer." sarcastic remark as this went ot very quickly.

 

[felten]

glad i dropped the little "only if you really like oxidised beer." sarcastic remark as this went ot very quickly.

Yeah that got kind of brutal... like a geek's thunderdome, 2 scientific arguments enter, 1 leaves

not that I'm knocking the information, it's very interesting

 

[skippy]

It in a way has been done and still is. The fermenting wort is roused by and external pump and the yeast is kept in suspension resulting in better attenuation and faster turn around. I think it was first done in the NZ land. Goggle continuous fermentation.
GB

continuous fermentation?

 

[Thirsty Boy]

[Edit: Just checked - aren't you studying this? Shouldn't you know this?]

yes I am, I do - and there are a number of things you have missed which make you wrong. Keep looking.

 

[drsmurto]

Back to the OP.

Get a real stirplate, not something driven by a computer fan.

Combine that with a 10+cm stir bar.

Very good chance you could get a vortex in 20L.

 

[drsmurto]

I have just finished my stir plate for starters and I was anyone thought of 1 for the fermenter I would asume you go 240volt but the yeast would love you some one do it and I can say its was my idea.

sava