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Home Brew Forums > Home Brewing Beer > Fermentation & Yeast > Starter length of time on the stir plate?
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Old 01-15-2013, 05:37 PM   #11
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Quote:
Originally Posted by Hockeyhunter99
wouldn't the presence of oxygen give the little buggers the proper condition for propagation and not fermentation? isn't that what a stir plate does? keeps the oxygen content to where propogation would possible and keeps them from fermenting. so why would the yeast stop reproducing after 18-24 hours?

i am so confused have i been doing this wrong the whole time?
With a stir plate you will have a higher propagation/growth rate due to the presence of more oxygen as opposed to a starter just sitting on a shelf. When you combine oxygen, sugar and healthy yeast you WILL have fermentation. At some point you will run out of food for the yeast to consume and that will lead to the end of fermentation and maximum cell density, which generally occurs in the 24 hour range according to literature I've read.
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Old 01-15-2013, 06:48 PM   #12
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I agree with the recommendations above. I usually run the stir plate until the wort turns from dark brown to milky brown. A related question: once I put the starter in the frige to cold crash, how long before *most* of the yeast has flocculated out? I usually go until I can see through the wort.

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Old 01-15-2013, 07:17 PM   #13
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@bmac yeast will NOT ferment with O2 present, they go through respiration, the break down of sugar with oxygen present. both fermentation and respiration release CO2 but only one will allow for yeast to reproduce. there is more energy released (used) from sugar during respiration, giving the yeast the ability to reproduce. no O2 means fermentation, which means less energy. that energy that would have been used to make more yeast but it is instead stored in the bonds of alcohol. that is why alcohol burns at the correct concentrations

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Old 01-15-2013, 10:11 PM   #14
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@hockeyhunter99 i reread what i posted earlier and i did screw up on the fermentation statement. Aerobic=growth, anaerobic=alcohol. As for the time on a stir plate you will still reach maximum growth in a defined period of time, which from everything I've read is between 18-24 hours. I personally run my stir plate for 24-36 hours depending on what else comes up and screws up my brewing schedule. Not sure anything negative would happen if you ran it longer but i don't think there would be any real benefit either.

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Old 01-15-2013, 10:20 PM   #15
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I just did a 4 liter starter and had krausening happening for about 48 hours so kept the starter on the stir plate. After chilling decanting and pitching the wort took off withing a few hours, so I must have done something right.

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Old 01-15-2013, 10:29 PM   #16
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Quote:
Originally Posted by twalte View Post
Here is some good information from Yeast Calc on doing a starter. Looks like I will go to 24 hours with my stirplate as I was cutting it short at 12 hours.

I still need to find some ferm-cap S to stop the Kreusen from overflowing my flask. (not at my LHBS)

http://www.yeastcalc.com/careandfeeding.html
Have you asked your LHBS, or just looked and couldn't find it? Sometimes they just label it as "foam control".
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Old 01-15-2013, 10:37 PM   #17
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I thought that using a stirplate is not primarily for oxygenating the starter but rather to keep the yeast suspended and in contact with the sugar in the wort

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Old 01-18-2013, 06:31 PM   #18
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I thought that using a stirplate is not primarily for oxygenating the starter but rather to keep the yeast suspended and in contact with the sugar in the wort
I believe it does both. The yeast cells circulate through the wort, particularly across the top, where the oxygen is.
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Old 01-20-2013, 04:28 PM   #19
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Originally Posted by twalte View Post
I still need to find some ferm-cap S to stop the Kreusen from overflowing my flask. (not at my LHBS)

http://www.yeastcalc.com/careandfeeding.html
I have read some threads about people using baby gas x, which is sold with infant supplies, where they could not find ferm cap s.
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Old 01-20-2013, 05:57 PM   #20
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I am by no means an expert in this area, but here's my 2 cents for what it's worth. Based on what I've read and previous experience I leave my starter on the stir plate for 24 to 36 hours, or until I have krausen. I put it in the fridge as soon as there's krausen. Based on what I've read about yeast and fermentation it seems that reproduction happens as one of the first steps. By the time you have krausen reproduction has already happened.

When my starter gets to room tempurature on brew day it picks right back up where it left off and I see CO2 bubbles breaking the surface and krausen forming again. When I pitch it's literally fermenting instantly.

Using this method I've both hit my FG every time and sometimes shot well past my FG.

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