calculate washed yeast

[pmoneyismyfriend]

I have 150ml of washed yeast, fairly thick but not compact. Does anybody know how to calculate how many yeast cells are in this?

 

[novahokie09]

What's the percentage of yeast to liquid? A 10% solution should contain 250 million cells/mL while a 55% should contain 1.4 billion cells/mL (source: Wyeast). If it's compact yeast, then you can see up to 4 billion cells/mL. You also have to consider how much of the slurry is actually yeast, not trub.

You can always use a Whitelabs vial or even a Wyeast Yeast Nutrient vial to determine what percentage yeast you have present. Obviously, you'd want to place it in the fridge to allow all yeast to flocculate out.

Look at bottom page of this link to see what I'm talking about: http://www.wyeastlab.com/hb_pitchrates.cfm

Also, you can use Jamil Zainasheff's yeast pitching calculator to determine how much yeast is in a slurry. His calculator allows you to chose the slurry's density and specify how much of the slurry is actual yeast.
http://www.mrmalty.com/calc/calc.html

Using Wyeast's numbers, you will have between 37 - 210 billion cells (assuming 250 million/mL [10% slurry] to 1.4 billion/mL [55% slurry]). Jamil's yeast calculator estimates anywhere from 130 billion up to 500 billion for 150 mL slurry, ranging from thin to thick yeast cake. Without seeing what you have, I'd say you're likely in the range of 150 - 210 billion healthy cells in a 150 mL slurry. This is based on Wyeast range between 40% - 60% of healthy cells based on "trub content, age of yeast, strain, original gravity, etc."

Without doing a cell count on a sample, you're relying on a lot of assumptions. If you're going to go this route, it's best to select a method that you can repeat. Once you have consistent results, you can then use your method to adjust pitching rate.

 

[pmoneyismyfriend]

My total solution is about 210ml and I would estimate my yeast to be at 140ml, I was messing with that calculator on mrmalty.com but I guess I wasn't totally getting it. Thanks

 

[pmoneyismyfriend]

also with mr malty, it will give me a viability of my yeast based on the date of harvest, and the amount of yeast I need based on o.g., but I don't see a formula for determining how much yeast I currently have, like I said before maybe I just don't understand that calculator

 

[LLBeanJ]

It's all a bit of guesswork, but you can get a ball park estimate. Since the yeast has been washed, the concentration is going to be close to maximum and the non-yeast percentage is going to be close to the minimum. Mrmalty's concentration slider max's out at 4.5b cells/ml, so just go with that. 4.5b/ml x 140ml = 630 billion cells (give or take - I'd round it down to 600b). Next, enter the viability date (I'd just go with a week after it was pitched in the batch you washed it from) and multiply 600 x the viability percent and that will get you a close approximation of how many viable cells you have.

 

[pmoneyismyfriend]

That's a lot easier to understand, thanks

 

[novahokie09]

also with mr malty, it will give me a viability of my yeast based on the date of harvest, and the amount of yeast I need based on o.g., but I don't see a formula for determining how much yeast I currently have, like I said before maybe I just don't understand that calculator

MrMalty is intended to tell you how much slurry to pitch based on the volume and specific gravity of the wort you're pitching into and the conditions of your slurry (slurry density and % non yeast). However, you can use it indirectly to determine how much yeast you have.

So let's make some assumptions. First, let's assume you have 1.8 billion cells per mL and 10% non yeast particulates in the thick cake at the bottom. We would use 4.5 billion for the 140 mL, but since you have 210 mL total solution, you have ~67% yeast slurry This means you need to set the yeast concentration to 1.8 billion/mL and the non yeast to 10%. I arrived at the 1.8 billion/mL by extrapolating the data listed on Wyeast's site that I linked.

Now all you need to do is change the volume of wort you're pitching into until the yeast slurry converges to your actual slurry (210 mL in this situation). The standard setup into 5.25 US gallons of 1.048 wort lists 177 billion total cells and 112 mL of our slurry (1.8 billion/mL and 10% non-yeast). Increase the volume of the wort until it arrives at 210 mL slurry. I will save you the trouble, 9.8 gallons of 1.048 SG wort requires 330 billion cells. This is equivalent to 210 mL of yeast slurry from our specific slurry parameters (1.8 billion/mL and 10% non yeast).

This requires a few steps, but there's a much easier way to arrive at the same answer. Multiple the 1.8 billion/ml by the amount of slurry you pitch. As Wyeast mentions on their site, "Harvested slurry is typically in the 40% to 60% solids range. A home brewer can make a rough estimation based on this information and combined with consideration for all other factors involved (trub content, age of yeast, strain, original gravity, etc.)."

For a 55% slurry, you have 1.4 billion/mL. Extrapolating for a 67% (140 mL yeast/210 ml total volume), gives ~ 1.8 billion cells/mL. Then all you have to do is multiple 210 mL by the slurry density, and you will arrive at 378 billion cells. You can also add a non-yeast correction factor to account for all the settle particulates to not be yeast, just assume a 10/20% number and then multiple your volume of yeast by 90%/80%. From there, you can calculate the percent yeast solids and use the Wyeast site to calculate slurry density.

From that analysis, you probably have around 330 - 380 billion healthy yeast cells in the 210 mL of solution, just call it 350 billion. I would just mix the 210 mL solution and then pitch the appropriate volume to get your proper pitch rate. For instance, if you wanted to pitch 250 billion cells, just take 250 billion cells divided by 350 cells per 210 mL. This means you'd need to pitch 150 mL of a well-mixed slurry to the wort to arrive at 250 billion cells.