Starter length of time on the stir plate?

Do I leave my yeast starter on the stir plate until the end of fermentation? How do I know I'm done and ready for pitching?

I just started doing the same...so curious to see the answers. I stopped a few hours after the kreusen receded...about 12 hours.

I saw a white labs video on YouTube and the guy, who looks like he knows z thong or two about yeast, says that it is done in 18 to 24 hours. After that you're just beating them up.
If I recall from biology 101, fermentation is anaerobic meaning it doesn't take place on the presence of oxygen. I put all this together to mean, and I practice, 18 to 24 hours on the to reproduce then I let it sit for another 12 to 24 hours at room temp to feed then I put in the fridge for a day or so to fall out. This way the yeast reproduce under optimal conditions, then they are well fed, then they sleep until I need them again which is typically right away for a batch if beer or a bigger starter.
Disclaimer: I am a humble home brewer and don't have anything except heresay and conjecture to back this up. Im also not sure if this works like I think it does but I have made viable healthy sufficient starters this way. May be it's an accident, may be I'm doing it all wrong and I don't know anything about it but I'm sticking with what works and I would like to share. If somebody does know better I would also like to hear it

About 24 hours if you leave the foil loose. If the foil is tight, I find it takes another few hours to finish.

i don't think it matters as long as they are in suspension. i don't see how you are beating them up when they are microscopic. i have left the starter go for a few days. i usually look for a change in color of the starter. it will lighten and become thick with yeast.

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

Like others have said, i usually keep my starter on the stir plate for 24 hours and then another 24 hours at room temp. I cold crash in the fridge until brew day then let the starter sit at room temp, decant most of the liquid and pitch.

I've had it on the stir plate for 72-80 hours before with a 2L starter. There were obvious changes up to about 55 hours, with the starter becoming significantly more 'milky' - after that time any changes were not noticable to me. Killed the stir plate at the beginning of my brew day, dumped the whole starter in the wort, had ferrocious fermentation within a few hours.

From what I have come to understand (Wyeast and White Labs info) is that the yeast will be reproducing for 18-24 hours. After that you are not gaining in cell count, just continuing to ferment the starter wort. I have gone a little longer with no ill effects. If you are watching and see a delayed start you may want to go longer but if everything is normal there is probably no need to.

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?

Hockeyhunter99 said:

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?

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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.

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.

@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

@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.

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.

twalte said:

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

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Have you asked your LHBS, or just looked and couldn't find it? Sometimes they just label it as "foam control".

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

stellaontap said:

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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I believe it does both. The yeast cells circulate through the wort, particularly across the top, where the oxygen is.

twalte said:

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

Click to expand...

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.

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.