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anbowden · 01-30-2013, 12:11 PM

After looking on mrmalty's yeast calculator on the "Repitching from slurry" tab, it's got a slider for yeast concentration where thin is 1 billion cells/mL and thick is 4.5 billion cells/mL. Let's say I made a 1L yeast starter yesterday and I've put it in the refrigerator overnight. Today it looks like I have 100 mL of yeast slurry. How "thick" do you think my yeast slurry is concentrated?

Also, how many mL of yeast slurry are in a Wyeast smackpack? I know it's 100 mL of liquid, but how much is actual yeast?

Thanks,
Andy

WoodlandBrew · 01-30-2013, 12:18 PM

The slurry calculator is a nice idea, but way off in my experience. Viability seems to be mostly driven by abv of the beer it is taken from. See here:
http://woodlandbrew.blogspot.com/2013/01/abv-effects-on-yeast.html

Cell density is typically 1 billion cells per milliliter of thick settled slurry, but can vary quite a bit mostly due to protein mixed in with the yeast.

If it is yeast cultures with DME then 2 billion cells per ml is more reasonable.

anbowden · 01-30-2013, 01:10 PM

Quote:

Originally Posted by WoodlandBrew

If it is yeast cultures with DME then 2 billion cells per ml is more reasonable.

Is it possible to achieve 3 or 4 billion cells per mL?
If I'm examining this not from the yeast cake harvesting side, but rather the 1st generation yeast starter harvesting, how does the smackpack or vial mfg. date play into yeast cell concentration?

Thanks,
Andy

WoodlandBrew · 01-30-2013, 01:49 PM

The date has very little to do with viability. After months in the fridge there will be little to no change. The vitality may be low meaning it will take time to start, but the viability will be high, meaning you have plenty of living cells.

Experiments here:
http://woodlandbrew.blogspot.com/2012/12/refrigeration-effects-on-yeast-viability.html

The diameter of a typical yeast cell is about 7 to 10um. So the most you could pack into a milliliter is about 3-4 billion, although that's rarely the case. You are probably looking at a density closer to 2 billion per ml.

anbowden · 02-02-2013, 02:32 AM

I've found some more information that would've answered my original question here(albeit with information that doesn't necessarily jive with your experiments):
http://www.mrmalty.com/calc/repitch.html

But I've been thinking about this more and more, and I've looked at some different scenarios.
Given: 1 packet of Wyeast 3068(Weihenstephan) dated 12/26/12 in a 3.5L starter with intermittent shaking

Scenario 1(using YeastCalc):
Viability from date: 71% -> 280 B cells

Scenario 2:
Viability not from date: 97% -> 332 B cells

I've actually already made this starter and it's chilled, now yielding a 200 mL slurry.

Scenario 3:
Yeast concentration from Mr. Malty: 2.4 B/mL (default for chilled starter) -> 480 B cells

Scenario 4:
Yeast concentration from Woodland: 2.0 B/mL -> 400 B cells

So using these different tools and different pieces of information leads me with a wide range of predictions. Obviously I'm not as interested in Scenarios #1 and 2 because I now have a known amount of yeast slurry I've produced, but it's still a little troublesome for me. What are your thoughts on this? I suppose it's very possible I'm overlooking something. It's important because I'm trying to harvest some yeast for a future brew day, and I want to make sure I divide the slurry properly.

On a sidenote, I'm really enjoying your website. Lots of good information and testing there.

Thanks,
Andy

WoodlandBrew · 02-02-2013, 12:42 PM

Thanks Andy,

I appreciate that you are looking around an not just taking what I say as golden because it sounds technical. There is more to yeast health than viability, and I think this is where Jimal creates some of his numbers from. There is a concept of "effective viability" that attempts to show the amount of healthy yeast that would be equivalent to the unhealthy yeast. I haven't done enough research or experimentation to come to a conclusion on this, but so far I have seen that unhealthy yeast and healthy yeast do preform slightly differently but have not seen any results that show there may be a use for "effective viability"

The cell counts you are getting don't seem to be to far apart. It looks like 373 +/-27% That's really not to bad for an estimator.

anbowden · 02-04-2013, 05:28 PM

Quote:

Originally Posted by WoodlandBrew

The cell counts you are getting don't seem to be to far apart. It looks like 373 +/-27% That's really not to bad for an estimator.

I guess that's a good point, it's +/-27% because it's only an estimate.
I'll be looking forward to more of your research/experiments to see if you draw a conclusion on healthy/unhealthy yeast.

Thanks again,
Andy

WoodlandBrew · 02-04-2013, 06:02 PM

Quote:

Originally Posted by anbowden

I guess that's a good point, it's +/-27% because it's only an estimate.
I'll be looking forward to more of your research/experiments to see if you draw a conclusion on healthy/unhealthy yeast.

Thanks again,
Andy

Preliminary results show that, surprisingly, the month old yeast out preformed the yeast from a starter in both attenuation and number of cells generated. And it doesn't look like a fluke. It's true of all 21 matched pairs, and it's not marginal. It Might be due to the glycogen content of yeast cells repiched at high krausen. There might be something to the "cold pitch"