Author Topic: Rousing Yeast  (Read 7013 times)

Offline ndcube

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Re: Rousing Yeast
« Reply #15 on: November 23, 2009, 07:51:22 AM »
Wouldn't it be easier to rouse yeast just by screaming, "Hello, Yeast!"? :D
That method rarely worked with my kids

My kids listen better when I whisper  ;D

[whispermode] hey, yeast you gots more sugars to eat according to the fast-ferment test data..[/whispermode]


Glad my hearing's pretty good.  I almost didn't hear that. ;D  Reminds me I want to try it for the first time today!

Offline bonjour

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Re: Rousing Yeast
« Reply #16 on: November 23, 2009, 11:08:12 AM »
Isn't the purpose of the stir plate to make more oxygen available to the yeast?  Just curious because I don't use one at the moment.
The stir plate performs several functions,  Keeps CO2 out, Adds O2, and keeps the yeast in suspension.

Fred
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Offline dhacker

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Re: Rousing Yeast
« Reply #17 on: November 24, 2009, 01:33:00 PM »
The stir plate performs several functions,  Keeps CO2 out, Adds O2, and keeps the yeast in suspension.

Fred

I wish someone would explain how a stir plate adds oxygen. I've heard this for years, but never could figure out how it's possible. If you mean making the already dissolved oxygen easier for the yeast to get at hence greater reproduction, yeah . . OK. But adding O2 as if pulling it into the flask from the outside world??  ???   Not convinced!
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Offline a10t2

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Re: Rousing Yeast
« Reply #18 on: November 24, 2009, 05:18:50 PM »
I wish someone would explain how a stir plate adds oxygen. I've heard this for years, but never could figure out how it's possible. If you mean making the already dissolved oxygen easier for the yeast to get at hence greater reproduction, yeah . . OK. But adding O2 as if pulling it into the flask from the outside world??  ???   Not convinced!

It's because the yeast scavenge O2 that's dissolved in the wort. Leaving the flask open to the air keeps O2 going into solution to replace what they're using. So they effectively have an unlimited supply of oxygen.
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Offline dhacker

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Re: Rousing Yeast
« Reply #19 on: November 24, 2009, 05:29:18 PM »
I figured that was the reasoning. But is a vacuum actually created to draw in O2? How?

 If CO2 is heavier than O2, how would the oxygen have any chance of displacing the CO2 from above? I'm just sayin', the physics seem cloudy.
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Offline bonjour

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Re: Rousing Yeast
« Reply #20 on: November 24, 2009, 07:09:01 PM »
the top of a flask is not sealed with a bubbler, the volume of CO2 produced is low when compared to a beer.  thus the air will try to equalize with the CO2 rich air in the flask,  The stirring will allow the liquid to to maximize it's absorbtion.  You don't need much

Fred
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Everything under 1.100 is a 'session' beer ;)

Offline dhacker

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Re: Rousing Yeast
« Reply #21 on: November 24, 2009, 08:45:48 PM »
the top of a flask is not sealed with a bubbler, the volume of CO2 produced is low when compared to a beer.  thus the air will try to equalize with the CO2 rich air in the flask,  The stirring will allow the liquid to to maximize it's absorbtion.  You don't need much

Fred

I know a lot of folks swear by their stir plates, I'm just having a hard time wrapping my head around the idea of air/ CO2 equalization ???, and that the stir plate is responsible for drawing in such minuscule amounts of oxygen and propagating the yeast cells so well as a result. As much as we harp on blasting the heck out of our fermenters with pure O2, seems odd a stir plate could do so much with so little!  :)
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Offline dhacker

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Re: Rousing Yeast
« Reply #22 on: November 25, 2009, 06:37:42 AM »
Someone sent this my way . . Thank goodness I was able to learn something today!  :D

http://www.chm.davidson.edu/vce/gaslaws/DaltonsLaw.html

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Offline tom

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Re: Rousing Yeast
« Reply #23 on: November 25, 2009, 03:28:14 PM »
Yes, the Law of Partial Pressure for gases. Each kind of gas within a mixture will equalize its concentration/pressure between the 2 spaces. Thus, as the yeast use O2 inside the flask its concentration (and thus partial pressure) will decrease. Because the O2 partial pressure is less than outside the flask, oxygen will diffuse into the flask. This happens independent of other gases' partial pressure.
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