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Author Topic: Stirred starter propagation rate  (Read 690 times)

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Offline djmitche

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Stirred starter propagation rate
« on: December 31, 2013, 11:07:42 PM »
W&Z's "Yeast" book gives some good data on propagation rates based on innoculation rate at 1.030.  Then the authors say "If you are using a stir plate .. the yield will be higher."  Thanks guys.  How much higher?  Empirical answers I can find online vary from 1.53x (mrmalty.com) through 10-15x (http://www.pivarstvo.info/forum/files/yeast_propagation_and_maintenance_128.pdf).  Looking at figure 1 in the latter shows a 5x increase in cell count for stirring over occasional shaking.

I started with some yeast from the end of October, so about 50% viability, or 50 billion cells.  I pitched this into 2L of 1.030 wort, for a pitching rate of 25 million cells/ml.  W&Z's figure 5.5 gives a doubling factor of 1.8, meaning that I have added 1.8x50 = 90 billion cells, for a total of 140 billion.  However, that's for an un-aerated starter.  Since I used a stir plate, instead I have somewhere between 214 billion and 2.5 trillion cells, with MB Raines' 5x putting it at 700 billion.  So that's pretty unhelpful!

Now, I'm happy to RDWHAH and pitch what I've got, but the engineer in me wants to know what's actually happening.  Does anyone have any guidance?  Or suggestions to how I could measure this myself without the expense of a cytometer?  Perhaps a graduated cylinder, cold-crashing, and some heuristic for the density of compact yeast cake?

Offline Ryan Hope

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Re: Stirred starter propagation rate
« Reply #1 on: January 01, 2014, 10:41:13 AM »
You don't need to do any of this your self. Its already been done. I find the the K. Troester stir plate growth adjustments are best. http://www.mrmalty.com/ doesn't support this but yeastcalc.com does.

Offline djmitche

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Re: Stirred starter propagation rate
« Reply #2 on: January 01, 2014, 11:13:56 AM »
I know I don't need to, but I like to understand what's going on rather than just plugging numbers into some JS script.

That K. Troester link is what I needed, and sure enough yeastcalc gives me a reasonable answer (338bn cells).

Offline MJDonnelly

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Re: Stirred starter propagation rate
« Reply #3 on: January 01, 2014, 11:15:53 AM »
I'm not nearly as curious as Dustin, so the YeastCalc calculated is great for me.  No more guessing on how much DME to use.

Thanks for the link Ryan!
Always drinking, never drunk.

Offline djmitche

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Re: Stirred starter propagation rate
« Reply #4 on: January 01, 2014, 11:19:33 AM »
To be clear, once I understand it, I'm happy to use a tool :)

Offline Ryan Hope

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Re: Stirred starter propagation rate
« Reply #5 on: January 01, 2014, 12:02:03 PM »
I know I don't need to, but I like to understand what's going on

Sure as do I, just saying you don't need to reinvent the wheel.

Offline TheRealDylanJohns

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Re: Stirred starter propagation rate
« Reply #6 on: January 02, 2014, 01:01:28 PM »
Now, I'm happy to RDWHAH and pitch what I've got, but the engineer in me wants to know what's actually happening.  Does anyone have any guidance?  Or suggestions to how I could measure this myself without the expense of a cytometer?  Perhaps a graduated cylinder, cold-crashing, and some heuristic for the density of compact yeast cake?

You can definitely do this, and that is probably your best bet if you aren't aiming for an absolute cell count. Density of the cake, cell size, and %flocculated will differ by strain, but not significantly for what you are interested in. If you get a decent sized graduated cylinder you should be able to transfer, cold crash, and measure easily. There are multiple sources for slurry volume to cell count, but I believe the conservative estimate is ~1 billion cells/mL.

This is a good idea for getting hold of how your personal stir plate/starter wort/nutrient strategy translates to growth. The problem with many of the 'studies' you read online are that 1) they are small scale, and 2) relevant variables are not always stated or adjusted for. For example, the guy with a lab quality stirplate pitching to 1.050 wort @ 76 degrees will see a lot more growth versus control than the guy with a homemade stirplate pitching to 1.036 @ 68 degrees.

Obviously initial viability and strain play a large part in this, but if you have a strain you usually stick to this will help you calibrate your own starter technique.

Offline Ryan Hope

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Re: Stirred starter propagation rate
« Reply #7 on: January 02, 2014, 01:28:39 PM »
The yeast slury calculator on Mr. Malty is pretty good at estimating cell counts.