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Yeast Starter on a stirplate

N

Neild5

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When making a starter on a stir plate is it better to run the stir plate continuously at a slow speed or just run it at a high speed to aerate every couple of hours?  I am not worried about burning up the stir plate as it is a heavy duty stirring hot plate just wondering which is best for the yeast.
 
You can run it continuously at a speed that is comfortable for the container and the stir plate.  You  don't need to crank it up as far as it goes as long as the surface is in motion and you have means for air to get in to the container.    Don't use an airlock!  Another factor to consider is the amount  of heat that the stir plate adds to the starter.    I have measured my starters at 7 F higher than ambient.  Part of the heat is from the exothermic reaction during yeast growth the remainder is from the stir plate.  Be aware of your ambient temperature.
 
IMO stir plates have little to do with aerating, once the yeast is blowing off CO2 short of bubbling oxygen or air into the starter no oxygen is getting to it. I've tasted my starters and while they're not a good beer it's because it's a bad recipe not because they're oxidized.
There's also a little thing called the Pasteur Effect saying yeast doesn't use oxygen once fermentation starts.
Again IMO stir plates are about keeping the yeast suspended to put off deciding they're at critical mass.

With this thinking I run it at full speed for about 15 minutes to aerate and then continuously at slow speed until I pitch.

But if you're convinced it's about aerating either way works. Aeration is at a very small level, it's about surface exposure not bubbles. Bubbles are exposing surface to air but you'll be getting plenty of exposure from the stirring.
 
The Pasteur Effect happens when the yeast begin to reproduce anaerobically. The OG I've seen associated with this is 1.040 and greater. By using OG of 1.020 to 1.030 in your starters will allow the yeast to continue to produce aerobically and using a stir plate to keep O2 defusing into solution is a good thing. For my 2L flask, I just cover it with a sanitized 250ml beaker to allow some airflow. My 5L flask is too big so I loosely cover it with sanitized aluminum foil. You don't want to use an airlock if you are using a stir plate. You will only need a small dimple to keep everything in motion for good oxygen exposure.
 
Run it at a medium-low speed.  Just when it starts making the whirlpool vortex in the middle, and then back it off a little.  Remember, the stir plate is for keeping the yeast moving and growing so speed is not the objective.
 
I would say a minimum of 24hrs, but if you plan ahead enough to go 48+ hrs that is best.  My problem is the planning ahead :)  I usually end up making it the day before and delaying my brewing til afternoon to give the yeast maximum time to grow.
 
Spin until the food is gone and yeast cell growth/count is maximized.  After that, it's just spinning. 

So, depends on amount and gravity of wort in flask.

If you pitch the entire thing, I guess it doesn't matter.  Some people chill and decant the spent wort and pitch only the cleaner slurry of yeast. 
 
MaltLicker said:
Spin until the food is gone and yeast cell growth/count is maximized.  After that, it's just spinning. 

So, depends on amount and gravity of wort in flask.

If you pitch the entire thing, I guess it doesn't matter.  Some people chill and decant the spent wort and pitch only the cleaner slurry of yeast.
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Yeah, I have heard of folks doing that too.  My theory is that I want the yeast suspended in the wort and pitch the whole thing.  My typical is 2L in 10gal.
 
Yep, that works.  The difference would be the style of the beer you are brewing.  If it was a lighter, delicate style, you might prefer to pitch just yeast slurry so spent wort does not affect the beer.  Porter, stout, it's likely covered up.
 
Kevin, honestly I go by the time rule......after about 48hrs the yeast is done doing it's thing.  I suppose you could get really technical about it (as with anything) but I try to keep to the K.I.S.S rule.
 
I run the stirplate at a minimum speed fast enough to create a vortex. I've also learned that you can split and refrigerate yeast starter over and over by transferring to sanitized containers. This has worked better for me than harvesting/washing yeast from the bottom of a carboy after fermentation. Splitting a yeast starter from dry malt extract allows you to keep more of the desirables, with fewer "undesirables".
 
I try ro start my starter 24 hours before I brew but usually forget and have about 12 hours.  I keep it as simple as possible.  I keep the spinning action just below a whirlpool so my yeast don't get too dizzy and like to have the starter in a pleasant environment with calming tones.  We are all pushing the yeast to work, work, work.  I want them to be happy too.  To my yeasty boys, I'm like, Relax, make a homebrew.

I have chilled the starter and pitched just the creamy slurry stuff and pitched the whole thing making my carboy too full.  I have never split a starter but do often repitch from the carboy.  Third repitch to 6th repitch seems to be my sweet spot making the best beers. 

When I repitch from the carboy, typically I will boil 1.25 liter water and chill covered.  I transfer .75ml of slurry from the carboy and mix well.  I chill this. Before pitching I decant off the water and slowly  pitch the yeast layer and discard the trub.

I have not had an infection that was noticeable before finishing the keg.  I am sure there are spoilers in there but the beer goes fast enough they never make a scene.

 
MikeinRH said:
I run the stirplate at a minimum speed fast enough to create a vortex. I've also learned that you can split and refrigerate yeast starter over and over by transferring to sanitized containers. This has worked better for me than harvesting/washing yeast from the bottom of a carboy after fermentation. Splitting a yeast starter from dry malt extract allows you to keep more of the desirables, with fewer "undesirables".
Click to expand...

I like this idea and have considered it from time to time but never tried it.  Have you ever had a problem with splitting the starter?
 
Not yet. I started with 1800 ml ... used 600 ml for the first brew, and 600 ml for the second. I refrigerated the remaining 600 ml in a sanitized container and plan to add that to commence a new 1800 ml starter today. I had to use a blowoff tube for the first two batches. Like I said, this seems to be a lot easier than harvesting or washing yeast from the bottom of a fermenter. I figure, if it doesn't continue to work, I can always pitch a new vial of yeast and shake the heck out of it.
 
Suppose you take a white labs vial and make a 2 liter starter.  They say that will double the cell count.  So, the average vial is 100 billion cells.  That doubles to 200 billion.  Now you divide that into three pitches and you get 66 billion cells a pitch which is pretty low. 

 
Mrmalty suggests that on a stirplate you can get 420 billion cells in a 1.8 L starter.  That said, I would guess that at least one decant and repitch step would be required to grow a starter that dense.
 
Nope. As a matter of fact, I cooked up another batch of wort yesterday and added the remaining one-third yeast starter from the original. I've got 1800 ml's on the stirplate right now and plan to use 600 ml's of that for tomorrow's IPA. I'm going to leave the remaining 1200 ml's on the stirplate until Tuesday ... use 600 more ml's and refrigerate the 600 that are left. Then start the whole process over again.
 
MikeinRH-

Unless you have a microscope and a hemacytometer...you can't really know how many yeast cells you have in your starters.  All of the available data from the experts in this field says that you are probably growing a little less than 300 billion cell colony in your 1.8L starter if you are only doing a single step.  So, when you divide by 3, you are innoculating with around 100 billion cells. 

That's roughly the same as a vial, so if that's what you are going for, that's fine.  Nothing wrong with that....it is a little under pitching though.  On the other hand if you think you are getting 600 billion cells in that 1.8 L starter, I don't think you are.  Everything I've read says that you would need at least one and maybe two steps to get that many cells in 1.8 Liters.  Mrmalty and yeastcalc both agree with that statement. 

Again, nothing wrong with what you are doing...as long as you are happy with the results.  Just putting some estimated numbers to what you are doing. 

 
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