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Old 07-04-2012, 06:26 PM   #1
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Default 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?

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Old 07-04-2012, 06:29 PM   #2
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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!!!

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Old 07-04-2012, 07:40 PM   #3
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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.

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Old 07-04-2012, 07:55 PM   #4
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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?
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.
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Old 07-04-2012, 08:31 PM   #5
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Oxygen is bad for your brew once fermentation has started.
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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Old 07-04-2012, 10:01 PM   #6
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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.
Yes, for very high gravity beers I have aerated again within 24 hrs of pitching. But, I wouldn't go further than that.
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Old 07-04-2012, 10:30 PM   #7
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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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Old 07-04-2012, 10:45 PM   #8
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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.

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Old 07-04-2012, 11:23 PM   #9
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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.

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Old 07-05-2012, 01:54 AM   #10
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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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