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Old 10-30-2009, 06:51 PM   #11
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I know everybody says that a stirbar helps exchange oxygen, but without real evidence (anyone have a dissolved oxygen meter?) I'm not convinced.

IMO all a stir bar does is drive off the co2 that is in solution and keep the yeast in suspension.

Even if the top of a flask is left completely open (rarely the case) how is the oxygen getting in there once it is full of co2?

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Old 10-30-2009, 06:54 PM   #12
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Originally Posted by Revvy View Post
...The yeasties seem to swim around eating sugar and peeing alcohol and farting co2 good enough on their own without needing an amusement park ride to do so.
Great!.... Now I have coffee coming out my nose and down my shirt from laughing so hard when I read this!

Somehow I could just see an animated video on homebrewing with the "yeastie boys" doing their thing in a carboy!

Thanks for the chuckle!
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Old 10-30-2009, 06:54 PM   #13
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This is like the third person today who has asked this....weird.

Besides keeping the yeast in suspension, you use a stirbar to, in a sense, whip oxygen into the stater, because oxygen is important to good yeast growth, or reproduction. But once the yeast has reproduced, oxygen is actually bad for beer. That's why you aerate wort intitially (and maybe again before the 12th hour for extremely high gravity beers- search for those discussions) but unless you like the taste of wet cardboard, you don't want to whip any more oxygen into the beer.
mmm.... wet cardboard
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Old 10-30-2009, 06:54 PM   #14
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Ah! It's not a matter of disliking your explanation! I certainly did not mean to offend. I was just looking for a bit more of a scientific explanation than "Oxidized beer is not yummy" I was merely conjecturing and offering my thoughts on the situation
basically there is no reason to agitate the yeast ... I sometimes will call them little pansy bastards if the FG is a little to high . But I don't physically abuse them I just do it mentally
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Old 10-30-2009, 06:57 PM   #15
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Originally Posted by Bokonon View Post
I know everybody says that a stirbar helps exchange oxygen, but without real evidence (anyone have a dissolved oxygen meter?) I'm not convinced.

IMO all a stir bar does is drive off the co2 that is in solution and keep the yeast in suspension.

Even if the top of a flask is left completely open (rarely the case) how is the oxygen getting in there once it is full of co2?
Then YOU do it...make up a 10 gallon batch of beer....split it into two fermenters, pitch EXACTLY one packet of dry yeast into each batch....Spin one with a stirbar, leave the other alone. Bottle and come back in 6 weeks and see if half the batch tastes like cardboard.

Otherwise, ANYTHING we say is conjecture on our part...except for many of us, are conjecture is based on brewing experience and an understand of the role and risk of 02 in brewing.
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Old 10-30-2009, 06:58 PM   #16
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Why would you need to agitate an active fermentation ?
Assuming a closed fermentation (no exposure to O2 after fermentation begins), I can think of a couple of reasons:
  1. For high OG beers, to avoid having to "rouse" the yeast (e.g., walk the barrel).
  2. To hasten conditioning. Keeping the yeast in suspension would expose more by-products to a larger quantity of yeast in a shorter time, this reducing the conditioning period. Budweiser does this with beechwood chips (increases yeast exposure surface area).

Some of us plan to experiment with a "stir plate" approach for larger batches (5 - 10 gallon). The theory is sound and the equipment cost to test the idea is negligible.
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Old 10-30-2009, 07:15 PM   #17
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Both sides present good argument. However, I am guilty of swirling my fermenter in the final days in between gravity readings to ensure that all of the sugar (or whatever desired amount) has fermented out. I think that I haven't had issues with taste because I've done it so far in, that the fermentation is complete or near complete. I've never had to shake the fermenter to get signs of life in the first days of the fermentation because it's going crazy on it's own. It kinda sounds like the "pro shake the fermenter" side is worried about stalled fermentations. You must remember to rely on your hydrometer to check your fermentations and not the air lock/blow off tube. If my last statement was wrong, then disregard. The only time that I think a stir bar would do anything useful is possibly for high gravity batches in short cycles to ensure the yeast doesn't settle.

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Old 10-30-2009, 07:26 PM   #18
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Originally Posted by ImperialLover View Post
It kinda sounds like the "pro shake the fermenter" side is worried about stalled fermentations. You must remember to rely on your hydrometer to check your fermentations and not the air lock/blow off tube. If my last statement was wrong, then disregard. The only time that I think a stir bar would do anything useful is possibly for high gravity batches in short cycles to ensure the yeast doesn't settle.
I tend to agree, and the thing to remember is that most of the so-called stuck fermentation threads, weren't stuck fermentations at all. They were people who used the airlock and not their hydrometer as a gauge of fermentation. Once they actually took a reading the found their beer was perfectly fine.

Or they were underpitching or using a yeast with a tendency to stuck at certain gravities, OR they produced a lot of unfermentables in their allgrain batches...

or they were just impatient,, and wanted their beer to be someplace it simply wasn't at when they wanted it.

and honestly except for the rare actual 1.030 stuck, or the impatient brewer....all the swirling in the world is not going to get a yeast to eat a fermentable that isn't there anymore.

I'd like to see Lamarguy's experiment..but I will only believe it if it is done similar to how I mentioned...you cant do two different beers, and two different yeasts, you have to be using the exact same base wort, from the same brew session (not two seperate brewing of the same recipe), and a carefully measured out equal amount of yeast....that's why I suggested two dry packets...and weighed out to be exactly the same amount. Because even with splitting a half gallon or gallon starter into two equal batches there is no gaurentee that the same numbers of cells got into each batch. And the stirplates should be commercially made and NOT home made ones so there can be do variance in rate of rotation either.

But I am wondering.....in doing it with a 5 gallon batchdoes anyone think the stirbar and stirplate needs to be sacled up proportionately, of will the little 1" baby on the satndard plate be enough.
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Old 10-30-2009, 07:27 PM   #19
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I actually like a bit of oxidization to my barleywines and I have had to shake a saison like a baby mid-fermentation and it turned out just fine. It's all relative. I would never put a fermenter on a stirplate, but I am with ImperialLover in that sometimes yeast need to roused prior to a diacetyl rest. I know it sounds oxymoronic, but I love the complexity of specialty grains and I love a dry beer. So I find myself getting the last few points dropped out with a gentle (or sometimes not so gentle) swirl at the end of a single fermenter fermentation. No one has ever accused me of serving wet cardboard.

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Old 10-30-2009, 07:29 PM   #20
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I was just reading the Porter section of Designing Great Beers. Daniels says before gigantic porter vats were built, brewers used to "take the fermenter for a walk" to rouse the yeast. This essentially consisted of rolling the barrels around the yard.

Oxidation aside, I don't see the harm in doing it. If you aren't getting the proper attenuation, you should probably look at your pitching rates, and pre ferment aeration.

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