# How many billion cells are in 1 ml of cold crashed yeast at the bottom of a starter

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##### Well-Known Member
Simple question...I know there is not a simple answer.

But assuming we are homebrewing, without a microscope, and all we have is fresh yeast, a stir plate, and some DME. How do you guys go about gestimating the amount of yeast in the bottom of your starter after it has been crashed for a couple days? Or in other words, How many billion cells do you think you have in each ml of yeast?
I currently assume I have 3 billion cells/1ml of yeast; so if I had 100ml of yeast I would assume 300 billion yeast cells, enough to pitch into 5 gallons of 1.065 wort (at 1 billion cells per liter).

I understand mr.malty, or yeastcal, or any other pitching rate calculator on the web will tell you what you "should" have after the starter, but I want to know what factor people use if they are calculating the amount of yeast they have visually; 1 billion, 2 billion, 3 billion, 4 billion/ ml of yeast?

Any thoughts are welcome!

Hmm, let's do a small calculation, using the original WLP vials as a gauge.

The WLP vials contained around 30 ml of liquid and 100 billion cells. This would compact into a solid cake, about 1/2 of that volume (sometimes less). 100 billion cells in 15ml ==> ~7 billion cells per ml of compacted slurry.

It's hard to judge the small volume in the bottom of a flask or jar, so I weigh them.
Previously I've recorded the weight of all my empty flasks and starter jars. After cold crashing and decanting as completely as possible I weigh the flask again. The difference is the weight of my thick starter slurry. For example, the difference is 125 gr. I guess 1/5 is still liquid ==> ~100ml of compacted slurry @ ==> ~700 billion cells.

Hmm, let's do a small calculation, using the original WLP vials as a gauge.

The WLP vials contained around 30 ml of liquid and 100 billion cells. This would compact into a solid cake, about 1/2 of that volume (sometimes less). 100 billion cells in 15ml ==> ~7 billion cells per ml of compacted slurry.

It's hard to judge the small volume in the bottom of a flask or jar, so I weigh them.
Previously I've recorded the weight of all my empty flasks and starter jars. After cold crashing and decanting as completely as possible I weigh the flask again. The difference is the weight of my thick starter slurry. For example, the difference is 125 gr. I guess 1/5 is still liquid ==> ~100ml of compacted slurry @ ==> ~700 billion cells.

Interesting. I think the vials are 35ml, and for simplicity sake saying 1/2 of the vial is pure yeast when settled would be a fine place to start (I have read that not all strains are the same size and some would theoretically take up more or less room; but 1/2 is a fine assumption, since that's the type of answer I'm interested in).
With those variables; 1/2 of 35ml is 17.5ml of yeast, and that is said to contain 100 billion cells, which would imply every 1 ml of yeast in a vial would contain 5.7 billion cells (100/17.5 = 5.7). That math is pretty straight forward, but then I have never seen such a high number, 5.7/ml, when people talk about estimating cell count; I have seen between 1-4 billion/ml.
I use 3billion/ml when estimating, because it is made from a starter and not exactly rinsed so I assume most is yeast (rather than proteins, or hop material, ect). I believe the 1-4 is referring more to a rinsed yeast or yeast starter situation (not pure yeast from the lab; white labs or wyeast where you might see 5.7/ml) but I'm not certain.

Here is a fresh jar of yeast I made from a starter...
You can see it has, roughly, 40ml of "yeast" in it. I have been estimating that this is approximately 120 billion cells of yeast (40ml x 3billion = 120). With the white labs example it would be more like 228 billion cells (40ml x 5.7billion = 228). That's a decent difference, hence my question.
My beer doesn't have any big problems anyway...I'm just looking for a better understanding of the most important ingredient in beer and how others estimate their cell counts...fun fun.

I have a 10ml graduated cylinder that I fill with homogenized post fermentation starter wort.
Once the yeast settles (cold crash) I look into the cylinder at the cake to calculate the dense yeast at the bottom. All of this while the starter is cold crashing as well.
Say I have 1.5ml of yeast slurry from a 1500ml starter I multiply 1490(1500-10ml sample) x .15 = 223.5ml of slurry that will be settled in the bottom of my starter.
Now I generally count cells with a microscope but you can decide what number per ml you feel comfortable using and bodda boom bodda bing.
Going back over my numbers I would get 1.25-1.5 billion per ml.

I have a 10ml graduated cylinder that I fill with homogenized post fermentation starter wort.
Once the yeast settles (cold crash) I look into the cylinder at the cake to calculate the dense yeast at the bottom. All of this while the starter is cold crashing as well.
Say I have 1.5ml of yeast slurry from a 1500ml starter I multiply 1490(1500-10ml sample) x .15 = 223.5ml of slurry that will be settled in the bottom of my starter.
Now I generally count cells with a microscope but you can decide what number per ml you feel comfortable using and bodda boom bodda bing.
Going back over my numbers I would get 1.25-1.5 billion per ml.

That's a great method to estimate pure yeast volume!

Now the yeast count you got is that from the compacted cake after cold crashing and decanting as much as possible? 1.25-1.5 b/ml sounds too low. If correct, how would that translate to the settled yeast cake in a WLP tube?

I typically cold crash the 10ml sample for two or three days to let it compact well before I make my calculations.
Many times I have already used the starter before I make those calculations because I am relatively certain I have made enough yeast and doing the calculations is more for documentation and verification. If your not sure and think you may have to step again then you may choose to calculate/count before you pitch the starter.
As for the manufacturers packages go, this is all about cell density. If you homogenize a White Labs vial it is roughly 2.8 billion per ml and Wyeast Smack Pack is 800 million per ml assuming you are starting with 100 billion cells.
If you don't have a way to count your sample then you are forced to make an educated guess on density. Various collection methods will produce varying densities.
If you consistently collect in a certain manner (starter, fermenter, top crop) find a way to get a handful of counts done and use an average or error on the side of caution.

There are so many opinions on this subject and very difficult for a newbie to grasp the whole concept.

I have made a handful of starters. The last one did not grow much for some reason. I pulled it off the stirplate after 48 hrs because the stir bar was no longer spinning. I have a Stirstarter plate and it just doesn't seem powerful enough to make a 1L starter, which is what I make.

Not to hijack this thread, but is it best to cold crash the starter for a couple days then decant and transfer the yeast or transfer immediately after taking from the stirplate while the yeast is still in suspension?

I use Mr Malty and Brew United's calculator to determine how much yeast I need. I'm still not certain which is the best way to measure.
For instance, I mainly brew 2 & 3 gallon batches. Mr Malty shows 83 billion cells needed / # ml of yeast needed is 89.

Assuming 1 oz = 30 billion cells, I would need around 3oz of slurry. is this calculated assuming you transfer right after removing from the stirplate and before cold crashing? I would just measure out 3oz right after removing from the stirplate and once settled I should have enough yeast to pitch right? 3oz really doesn't seem like enough yeast. When it compacted I had less than a ML of yeast so that makes me think there was not a lot of yeast in suspension.

If you don't have a microscope then I would suggest using an online calculator that you trust or comes highly recommended and roll with it.
If the calculator has multiple growth models or slurry densities to choose from choose conservatively.
Calculating yeast is a crapshoot at best even if you have the proper equipment. Most of us use multiple strains all of which behave differently and even when using the same strain they will behave differently. Trying to count a very flocculant strain in a large propagation is a nightmare.
At the end of the day you don't want to grossly under pitch and you would have to work pretty hard to over pitch.

I found this recently and thought it was am interesting read.

http://www.experimentalbrew.com/blogs/saccharomyces/yeast-cultures-are-nuclear-weapons

Basically the conclusion is that as long as you're close, as in +/- 50% close, you shouldn't be too worried about cell counts.

That's a fun article for sure, "yeast is a nuclear weapon." If that is the case it pretty much equalizes the 1-4 billion cells per ml thought...as long as you were gestimating in that range you'd be ending up at the same finishing count anyway at the end of fermentation. Interesting.

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