Why not stir the fermenter?

I have learned that people use stir plates for making yeast starters. I don't know exactly why, but I guess it speeds up fermentation and increases attenuation. Why not make a big stir plate and stir the main beer fermenter? If it's a good idea for starters, why not for beer?

It's sorta OK to oxidize your starter but not a whole batch of beer. Might be OK for the first 18-24 hrs or so but not after that. Plus that would be one big ass stir plate and stir bar!!!

You provide constant aeration to your starter with a stirplate because your trying to make more yeast cels. With your fermenter your trying to make beer. Like Poobah stated. Oxygen is bad for your brew once fermentation has started.

BetterSense said:

I have learned that people use stir plates for making yeast starters. I don't know exactly why, but I guess it speeds up fermentation and increases attenuation. Why not make a big stir plate and stir the main beer fermenter? If it's a good idea for starters, why not for beer?

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You stir or aerate a starter because the yeast need o2 during the reproductive phase. Which is the same reason you aerate wort before pitching. If you continue to aerate (or stir) after the yeast reproduce they will stop consuming the o2, and the leftover o2 can/will lead to fast staling of the beer. Wet cardboard is the most common description for oxidized beer.

Hammy71 said:

Oxygen is bad for your brew once fermentation has started.

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It's a good rule of thumb, one homebrewers can't go wrong following, but it's not strictly true. Some breweries (Samuel Smith, for example) actively agitate and aerate their beer well after fermentation has started. It's not until late in fermentation, when sugar concentrations are low and the yeast begin to drop out, that you really need to start keeping things anaerobic.

corax said:

It's a good rule of thumb, one homebrewers can't go wrong following, but it's not strictly true. Some breweries (Samuel Smith, for example) actively agitate and aerate their beer well after fermentation has started. It's not until late in fermentation, when sugar concentrations are low and the yeast begin to drop out, that you really need to start keeping things anaerobic.

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Yes, for very high gravity beers I have aerated again within 24 hrs of pitching. But, I wouldn't go further than that.

Hmm what aeration? If fermentation has already started, is not co2 being produced and haven't other gases been pushed out of the fermenter? how is the stir plate is going to actively pull oxygen into the beer if its not in the fermenter? I call bunk on the above replies.
Seems like it would be an excellent idea for the first 24 hours.

Shea Comfort (www.yeastwhisperer.com) actually recommends it and rouses his yeast daily when brewing, just as winemakers do. He makes great beer and suggests that S. cerevisiae doesn't really know what it's fermenting so why not treat it the same in both cases. You can rouse yeast without aerating quite easily. I find it more of a pain to pull the pail of of my ferm chamber, pop the lid and stir so I choose not to at this point but I see no harm in doing it.

EDIT: Shea is a consultant to Lallemand so he does know yeast pretty well.

Stirring the fermenter under anaerobic conditions is also called rousing the yeast. Helps drive down FG a little bit and cause the early flocculating yeast to come back into suspension and drive off CO2. With an airlock on I wouldn't expect to oxidize the batch, so I don't think it should hurt, as long as the fermentation isn't open like with a starter and stir plate.

Well, looking through the stir plate thread, there were several people with massive stir plates that can handle a carboy. I can totally see dropping a stir bar in the carboy and setting it on a stir plate just in case you want to rouse the yeast some during fermentation. It sounds like some people do it.

BetterSense said:

Well, looking through the stir plate thread, there were several people with massive stir plates that can handle a carboy. I can totally see dropping a stir bar in the carboy and setting it on a stir plate just in case you want to rouse the yeast some during fermentation. It sounds like some people do it.

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I got one like that as a test product of a commercial unit. I'm not sure it can be done with a computer fan, though.

I guess in theory it can be done in the first 24-36 hours of fermentation, but if you have to do this to make good beer I'd say you have other problems.... IMO!
I don't have problems with attenuation, so I'd never do it.

Budzu said:

Hmm what aeration? If fermentation has already started, is not co2 being produced and haven't other gases been pushed out of the fermenter? how is the stir plate is going to actively pull oxygen into the beer if its not in the fermenter? I call bunk on the above replies.
Seems like it would be an excellent idea for the first 24 hours.

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What's going on here?I've never considered this angle before.

I'm pretty sure the same goes for erlenmeyer starters on stir plates.. there's not much if any oxygenation going on after fermentation starts.

I've done stirred 6 gallon carboys, but the best vessel for this is the sankey keg. 1/6 bbl or 1/2 bbl, they work great with a 2.5" stir bar in the perfect bottom center of the keg. I use them for starters for 2 barrel batches. It is a large dc computer fan that I use, with 7-9 volts.

There is stirring and then there is aeration. Not all stirring is aeration. Once you put the airlock on to prevent any more oxygen from coming in, you are just stirring, not aerating.

The yeast themselves do a pretty good job of keeping things roused up so a stir plat isn't really necessary. However, if you want to go for it, it won't cause any harm to the beer.

There are a few yeast that are notorious for dropping out early, and if using one of these yeast, then there might be some benefit (although the occasional swirl would probably be enough)

Stirring a carboy that has an airlock will not oxidize anything.
One thing not mentioned here is the effect of CO2 on ester production. I will guess you may get more esters by driving off CO2, but the esters may go with it.
Try a side by side that would be fun.

It could certainly be a good idea once reproduction is over... more yeast exposed to the wort for 'mellowing.' Artificial bechwood aging. If the fermenter is sealed you don't have to worry about O2. Stirring would also eliminate thermal stratification, which, if you've played around with immersion chillers and multiple thermometers, is very significant.

I'm very interested in stirring to eliminate thermal stratification. My one concern is whether it would increase fermentation of proteins and other undesirables that have settled at the bottom of the vessel. I recall that John Palmer advises against leaving beer in primary for that reason. It would also eliminate the ability of the brewer to transfer to secondary and with that transfer leave behind the same proteins and other undesirables. Thoughts?
Truly temperature controlled fermentation in home brew is something of a dream of mine. Ideas I have, barring a solution to this issue:
- Really wide fermentation vessels
- Immersing the fermentation vessel in a well circulated liquid e.g., water to keep it well temperature controlled throughout by convection

I'm leaning toward option 2 above once I have a big enough place to put it together.

To address the transfer issue you mentioned, from my experience doing this it should not create a problem, as long as you can stop the stirring.

The reason is, it will speed your fermentation, causing the yeast to flocculate earlier. If you can see the ferment, you may notice when the yeast tries to cling together to drop out. At this point (or a day before you desire to transfer), you can stop the stir, chill a bit if possible, and everything will settle out very quickly after, allowing you to cleanly transfer. Its similar to what you'd expect decanting a starter. So it also depends on the yeast strain.

Another good thought to home brew fermentation - buy a refrigerator big enough to stick your fermenter into. I brew in fl and its hot! Indoor temps of 78 degrees sometimes still fermenter my beer strong! However the refrigerator can be controlled with an on off switch, but it on low and control the beer fridge. A solution to heat ferment refrigerator

Andrewskibrewski - Even inside a fridge I will still have temperature stratification just as if you had a fermenter in a well-ventilated basement at the apropriate temperature. Some kind of convection (stirring inside, or fluid motion outside, or both) is really what I am looking for, as opposed to conduction cooling.

Budzu: Will that solve my non-yeast particles, though, that drop out immediately after the boil for example? I'm not going to re-boil after primary so even cooling rapidly I'm not sure it will have quite the same effect.

afsjoiwejio said:

Andrewskibrewski - Even inside a fridge I will still have temperature stratification just as if you had a fermenter in a well-ventilated basement at the apropriate temperature. Some kind of convection (stirring inside, or fluid motion outside, or both) is really what I am looking for, as opposed to conduction cooling.

Budzu: Will that solve my non-yeast particles, though, that drop out immediately after the boil for example? I'm not going to re-boil after primary so even cooling rapidly I'm not sure it will have quite the same effect.

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I think that during active fermentation (the time when temp control is most critical) the yeast do a pretty darn good job of stirring up the wort, so I really don't think you would get much temp stratification, I could see it happening after fermentation, but I don't think it would be to extreme if unless the water/air around the fermenter also has some serious stratification.
Just my two cents.
Chickens

afsjoiwejio said:

Budzu: Will that solve my non-yeast particles, though, that drop out immediately after the boil for example? I'm not going to re-boil after primary so even cooling rapidly I'm not sure it will have quite the same effect.

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I'd think those particles will act the same stirring/stopping as if you did not stir. They should sink pretty fast, usually faster than the yeast. Are you getting alot of trub in the fermenter and trying to find a way to keep it out of the finished beer? I think that's a different issue that this technique doesn't address.

Stirring high gravity wort increases esters. Stirring low-gravity wort decreases esters.
http://www.draymans.com/articles/arts/18.html

I just let my sit, I appreciate the knowledge however...I never ever thought about stirring it. Sitting the barrels of beer and keeping it still was what I thought the best idea