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Old 03-15-2011, 12:39 PM   #1
stunsm
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Default Stir plate efficiency

So how much does a stirplate really increase cell count? I've read some posts and literature that claim up to a 10 fold increase, but the Wyeast calculator seems to show only about a 30% increase. I've used a stirplate on all of my starters and have always had very vigorous fermentation, but I'm curious what the real effects are, and if the 30% figure is accurate, I've been grossly underpitching but still getting very good results.

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Old 03-15-2011, 01:10 PM   #2
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That depends on what you're comparing it to. It's about 30% more than "shaking the starter every hour." It's probably twice as many as a straight starter that isn't touched after pitching.

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Old 03-15-2011, 01:44 PM   #3
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I was wondering this thing myself. I use the "shake when you walk by" method with great results. However, a stir plate IS a cool piece of gear...

Pez.

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Old 03-15-2011, 03:01 PM   #4
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I've used the calculators at mrmalty and wyeast, but they seem to give slightly different results. Anyone with a hemocytometer ever do any side by side analysis?

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Old 03-15-2011, 05:29 PM   #5
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I too am interested in hard data regarding the effectiveness of stir plates. Specifically, how does O2 get into the starter after fermentation begins and CO2 starts billowing out?

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Old 03-15-2011, 05:37 PM   #6
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Quote:
Originally Posted by Pivovar_Koucky View Post
I too am interested in hard data regarding the effectiveness of stir plates. Specifically, how does O2 get into the starter after fermentation begins and CO2 starts billowing out?
Never thought of that very interesting point.
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Old 03-15-2011, 06:42 PM   #7
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Originally Posted by 724b View Post
Isn't O2 constantly getting absorbed because of the movement? That's one of the reasons that growth rates are so much higher with a stir plate.
But when it is fermenting it produces co2 which would push the o2 out of the container...the co2 blankets the wort
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Old 03-15-2011, 07:11 PM   #8
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People believe that because CO2 is denser than air it forms a distinct layer, but this is just not true. There's CO2 in air... it moves around and gets incorporated.

CO2 and air are not oil and water, they're honey and maple syrup - eventually they mix.

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Old 03-15-2011, 08:11 PM   #9
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Originally Posted by kanzimonson View Post
People believe that because CO2 is denser than air it forms a distinct layer, but this is just not true. There's CO2 in air... it moves around and gets incorporated.

CO2 and air are not oil and water, they're honey and maple syrup - eventually they mix.
Yes, but they mix by diffusion or by convection. If you have 1 liter of wort at 20 degrees C (68 F) and the gravity goes from 1.040 to 1.010 then you make 16.67 L of CO2. If that takes 48 hours then you're talking 347.3 cubic centimeters per hour. Unless O2 can diffuse against that flow rate, CO2 will quickly push all of the O2 out of the flask.
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Old 03-15-2011, 08:17 PM   #10
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I'm curious if there's a correlation between the way liquid moves in the starter and the way gas moves in and out of the flask.

What I mean is, the whirlpool of the starter creates a lower pressure region in the center of the flask. Does that mean that more CO2 is leaving the center of the starter, in general? Or do you think this is a negligible effect? If it's true, perhaps more O2 is able to enter the liquid at the edge of the surface?

Just throwin out some pseudo-science here...

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