Washed Yeast - How to figure slurry volume?

As I don't yet have the equipment to slant yeast, I've been washing yeast I wish to save both from a carboy and a starter (for bottle harvested yeast). Because fridge space is at a premium I'll often take it once step further and once all the yeast has settled down in the quart jars I'll boil water & baby food jars, decant off a lot of the liquid in the quart jars and swirl up and transfer the yeast to the baby food jars.

The process works great, but I'd like to be more precise about making proper starters using either mrmalty or yeastcalc.com which means I need to know the volume of slurry.

I've attached a picture example of a baby food jar of harvested Rogue Pacman yeast. Is there any forumla I can use to determine that volume of slurry without having to resort to decanting, swirling and pouring into a very small graduated beaker?

That shape looks like a small cylinder. The volume formula for a cylinder is V=[pi](r^2)h which you could determine the height and radius using a measuring stick. Thats how i would go about it, but i have not done slurries and i am assuming you want the volume of the material within the container.

Since you have to guess to determine the viability of your yeast, having an exact volume isn't really necessary. Make a starter and RDWHAHB.

Just put another jar next to it, fill it with water until it is even with the yeast level in the other jar, and then measure the water amount.

beerkrump said:

Since you have to guess to determine the viability of your yeast, having an exact volume isn't really necessary. Make a starter and RDWHAHB.

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Yes, I could simply RDWHAHB but I keep reading that one of the turning points into making consistently good beer is pitching proper amounts of yeast.

Mr Malty slurry tool shows between 2.5 - 3.5 billion cells per ml depending on the thickness of the slurry (mine is fairly thick). If I know how much slurry I have I can conservatively estimate how many billion cells I'm starting with, which I can then plug into either yeast starter calc tool and figure out how many starters of which volume to make.

TO me that's valuable information as I like to make small starters and step them up when pitching a small washed slurry.

pabloj13 said:

Just put another jar next to it, fill it with water until it is even with the yeast level in the other jar, and then measure the water amount.

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Thank you! I had a feeling I was over thinking it and while not exact it's a reasonably 'good enough' starting point.

pabloj13 said:

Just put another jar next to it, fill it with water until it is even with the yeast level in the other jar, and then measure the water amount.

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Extra points for not using math!

Check out this website.
http://seanterrill.com/2010/03/23/yeast-ranching-and-you/

Sean does a great job decribing the process and calculating the volume of your slurry.

Here is the formula to calculate the number of viable yeast in your jar.

∏(Radius cm²)(Height cm)(density of yeast in billions)(Viability)= Viable Yeast Cells

Gregscsu said:

Check out this website.
http://seanterrill.com/2010/03/23/yeast-ranching-and-you/

Sean does a great job decribing the process and calculating the volume of your slurry.

Here is the formula to calculate the number of viable yeast in your jar.

∏(Radius cm²)(Height cm)(4.5 billion)(Viability)= Viable Yeast Cells

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The problem is that there is quite a curve to the bottom of the jars. Look at a mason jar, for example. The first gradation (100mL) is WAY farther from the bottom of the jar than the 200mL mark is from the 100mL mark. Plus, math is for engineers.

Just average the radius of the jar near the curve. The formula is not exact, but at least its a solid starting point, as opposed to a complete random guess.

Gregscsu said:

Just average the radius of the jar near the curve. The formula is not exact, but at least its a solid starting point, as opposed to a complete random guess.

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Or just pour water in another equivalent jar up to the yeast and measure that, like I said. No "random guesses", no calculators.

pabloj13 said:

Or just pour water in another equivalent jar up to the yeast and measure that, like I said. No "random guesses", no calculators.

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Technically, using that method you still have to calculate the number of yeast per a ml and viability, to determine the amount of viable yeast.

Gregscsu said:

Technically, using that method you still have to calculate the number of yeast per a ml and viability, to determine the amount of viable yeast.

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Absolutely, just as you would with the mathematical method. I let MrMalty calculate viability for me and put non-yeast percentage at 10% and the yeast count at 3.5 billion per mL. Works well that way.

If you like math, like myself, you could split the jar into different symmetry operators. Looks like half a semi-sphere and a cylinder. That will get you a pretty accurate volume mesasurement. If you don't like math, then follow Pabloj13's suggestion and you should get a rough volume value that i think would be accurate enough for brewing purposes.

Points to pablo on the quick technique. I completely did not see that!

That is why I like to re-use my White Labs vials! I fill them up with yeast slurry and after a few days in the fridge they look (volume and color) exactly like vial straight from the lab. I just say each vial contains 100B cells (roughly).