I am wondering about how to use the Mr. Malty calculator for washed yeast. Should I treat it like liquid yeast or slurry?
The reason I ask is that I have been washing my yeast and storing it for up to two months. I store it in 2000 mL Ball jars- the yeast portion ends up being about 400-500 mL. The final product looks like a massive White Labs vial. The online calculator says that the liquid yeast is 54% viable after 2 months, and the yeast slurry is only 10% viable. I assume that the washed yeast is the slurry. However, I have seen no ill effects of time to ferment or attentuation that would be indicative of 10% viability.
Secondly, if washed yeast is somehow different from a vial of yeast, what magic is done to increase the viability?
As I understand it, yeast from white labs, wyeast and the like are all extra-carefully prepared and washed down with distilled water at the optimum level of dormancy. In other words, they do some stuff to extend the shelf-life of the yeast. I’ve definitely heard of some people using yeast that they rinsed themselves and kept refrigerated for months. I tend to use the repitch/washed part of the calculator, but crank up the supposed yeast density only measuring the compact bit at the bottom of the jar.
What if you’re rinsing it though? As in adding in say 2-3x the volume of cooled boiled water as you have slurry, swirling it up, and letting it settle out for a few minutes then pitching the liquid. It would be better to set it at a low non-yeast percentage and low yeast concentration, right?
Whatever methods gives you the most accurate count, and ime it’s using the settled yeast volume. If you took 100mL of settled yeast and mixed it with 300mL water I’m not sure it would look all that different than 200mL yeast + 200mL water once you shook it all up.
This is a question that I see all the time on homebrew forums and nobody seems to have a definitive answer for yeast count per unit volume of settled yeast. Or at least the ones that claim to don’t agree. We have yeast count but then we also have viability and non-yeast percentage numbers and everybody seems to be guessing at all three. It seems the yeast count of settled yeast part should be straightforward enough. Guessing at two variables is better than guessing at three.
There is a picture somewhere from Wyeast or WhiteLabs showing vials with different yeast densities in them; of course I can’t find it when I am looking for it.
That being said, I think it still really depends on the strain because some strains flocculate more compactly than others, etc. The bottom line is that the only real way to estimate counts are with a microscope. But in the majority of homebrew situations, this is totally overkill, just infer your counts by monitoring everything else you can (lag time, attenuation, flavor formations, off flavors, etc.) then use those other data points to adjust your pitching rate.
I typically do what I think Denny is suggesting, tell the calculator you are repitching from slurry, and go very pessimistic about the non-yeast percentage and the thick-thin slurry numbers are.
By a couple different methods, I concluded that a fully packed slurry will be about 4.3 billion cells per mL. Jamil Zainasheff, who’s probably as much an authority in this as anyone, says 4.5 billion/mL. So I think you could take that to be fairly accurate. Similarly, if you’re rinsing the yeast with sterile water, it seems to me - at least visually - that the non-yeast portion drops pretty darn low even after a single cycle. So figure 0-10% on that, make your guess at viability (25% loss per month, refrigerated and stored under beer/water is a pretty well-established figure) and you’ll probably get your overall cell counts within ±20% or so. That actually compares pretty favorably with typical use of a plate hemocytometer, and is good enough for our purposes IMHO. It’s only beer.
That pic just looks like vials of different amounts of settled yeast to me. The 25% one has ~2.5x the settled yeast as the 10% one and so on. It doesn’t look like it’s really telling you anything except how to eyeball 10% of a vial (or whatever). Am I missing something?
I agree with the above post… However, I did find the web page on Wyeast’s site. The photo of the vials is at the bottom of that page: http://www.wyeastlab.com/hb_pitchrates.cfm
I think what the image may be trying to portray is the amount of pure yeast in those vials as compared to a mixture of yeast/trub which people may have in their containers. Wyeast says you need 1.5 to 2 times the amount of yeast pitch from a slurry as compared to their normal pitch rate. I may be wrong about the photograph though…
Well, if I remember right, those are 25mL vials, so with the numbers (like 1.4e9) they’re also showing you what different pitching rates look like after they flocculate.
Thanks Anthony. I just went to that Wyeast page and it doesn’t say how big the vials are. Unless I’m doing my cipherin’ wrong (or the answer is over an order of magnitude different than the 4.5 billion/mL), they must be larger than 25mL. Using the 10% example: 10% of 25mL is 2.5mL which corresponds to 2.5E8 cells (i.e. 250 million). That’s only 100 million per mL.