Yeast Pitch Rates: Starters vs. decanted yeast

[kdw2pd]

I'm trying to make sense out of pitch rates, and need a little bit of guidance. I've used MrMalty, etc., for pitch rates, but am still struggling to figure out how it all works. The yeast I'd like to use is harvested Ommegang yeast, stepped up a couple times to a 2L starter, now decanted.


1.) How to figure out the pitch rate for decanted yeast. For example, a 5 gallon, 1.075 dubbel requires 257B yeast cells. Setting the "slurry" tab to 3B cells and 0% non-yeast tells me I need 88ml of yeast, or about 6 tbsp. Is that right, for fresh, 90+% viable yeast?

Alternately, with the "liquid yeast" setting set to require 1 vial of yeast, it requires a 1.6L stirplate starter. How much yeast is presumed to be present at the start? The 100B figure tossed around for fresh White Labs vials? Using the example above, would that mean I would need 33ml of yeast in the 1.6L starter (3B cells per ml * 33ml = ~100B cells)?

 

[WoodlandBrew]

3 billion cells per milliliter is probably a little bit high of an estimate. If the yeast was grown with DME it's probably closer to 2 billion cells per milliliter of thick settled slurry.

 

[troglodytes]

What I do is decant most of the starter leaving enough to get all the yeast into suspension and then estimate that full volume @ 1.2B cells per ml. Generally my results fall in line with the estimated Yeastcalc.co numbers calced at each step.

When I harvested Ommegang yeast myself last year. I used 25ml of very weak wort to wake the little yeasties up. At that point I said I had 500M viable cells. I then stepped it 3 times

After Step 1 (.1L @1.020) it calcs 8B cells
After Step 2 (.5L @1.025) it calcs 58B cells
After Step 3 (1.5L @ 1.035) it calcs 268B cells

Try to recreate the steps you did as you ramped up to get a good estimation of how many cells you have. It may not be exact but if you need 257B cells and the calculations are estimating that you have 268B, you are going to be fine.

 

[kdw2pd]

Is there a general rule for yeast density for dregs after waking them up in weak wort? For example, I just pitched the dregs of 2 bottles of Duvel into 75ml of 1.04 wort. I'm going to leave that on the stirplate for 3 days or so. What should my starting density for YeastCalc be, once I start stepping it up? 100 mill? 300? 500?

 

[WoodlandBrew]

Generally settled slurry is about 1.5 billion cells per ml, although despite what most of the calculators indicate, pitch rate doesn't greatly influence yield.

 

[butterpants]

Decant, count them then measure yeast n multiply right?

If you're making growth estimations based upon time and standard rates the error seems like it would be huge.

It's big enough counting with a hemocytometer.

For 200$ you can be making actual cell counts. Why half ass it? Get the 65$ bright-line hemocytometer from cynmar... it's a million times better than the cheap one.... even more so if you're using a 150$ microscope.

Am I crazy? In my mind without a spectrophotometer or cell counting (microscope + hemocytometer) you're just guessing.

 

[WoodlandBrew]

In my mind without a spectrophotometer or cell counting (microscope + hemocytometer) you're just guessing.

You are absolutely right. Using a yeast calculator or estimating by volume is often off by a factor of two.

 

[RM-MN]

You are absolutely right. Using a yeast calculator or estimating by volume is often off by a factor of two.

According to this experiment being off by a factor of 5 one way or another can still make you pretty good beer.

http://sciencebrewer.com/2012/03/02/pitching-rate-experiment-part-deux-results/

Are we fooling ourselves with the "precise" amount of yeast needed and our "precise" way to get that amount?

 

[WoodlandBrew]

Are we fooling ourselves with the "precise" amount of yeast needed and our "precise" way to get that amount?

Mostly yes. This topic really deserves a whole article.

 

[butterpants]

It's all about repeatable results. Can you rebrew and make the same exact beer, if need be? I think it's a goal we as brewers should be striving for. Sure I like surprises.... but when I spend my personal resources and knowledge, I expect a specific result. If I get something different, I may not necessarily be happy.

But then again I am a maniacal control freak