Repitching from slurry question

geocool · November 9, 2011, 8:45pm

So I have some saved yeast slurry (WY3724 Belgian Saison) that I plan to reuse. Brew day will be seven weeks after the harvest date. According to mrmalty.com the viability is 19% and therefore I’ll need 677ml or 22.9 floz of slurry per five gallons. This is 280 billion cells. My OG will be 1.082.

So lets say instead of pitching this straight in, I make a 3 quart starter one week in advance. Should I still use 22.9 floz of slurry in the starter, or can I use less because of the growth that I’d be able to expect? Again, using mrmalty.com it looks like I can get to 280 billion cells by simply pitching 88 billion (one pack at 88% viability) into a 3 quart starter. That would be only 7.1 floz of slurry in the starter.

So is this what I should do? Pitch 7.1 floz of slurry into a 3 quart starter, and then from there into my 1.082 wort? Have I made any mistakes?

560sdl · November 9, 2011, 10:02pm

This is all so confusing, so I feel your pain. I don’t have the specific answer and I find all the calculators so confusing. Especially when using slurry. I cannot even figure out what constitutes slurry. Is it raw trub off the bottom of a primary fermenter or washed yeast? Obviously those two things constitute entirely different concentrations if yeast per ounce.

baratone_brewer · November 10, 2011, 12:27am

I would estimate your viability as around 48% @ 7 weeks if stored under beer and refridgerated.

Depending on the thickness of your slurry and if your yeast has been rinsed, I would build a starter from 110ml for thinner slurry (2.5B/ml) or 65ml of thicker yeast (4B/ml). Then pitch into a 2.0L starter if using a stir plate. 3L starter if using intermittent shaking.

Should get you in the ball park.

brewmagician · November 10, 2011, 4:10pm

If you have 7 weeks, you could also brew an intermediate, 1.050 beer to ferment on it, then use that slurry for the big boy. Basically using a whole batch of beer as a starter. Then, you have more beer!

If you get really worried about it, fresh yeast will always do the trick.

a10t2 · November 10, 2011, 4:35pm

I’d second BB’s advice. The MrMalty calculator is ludicrously conservative when it comes to viability predictions, IME.

brewmagician · November 10, 2011, 5:29pm

+1 on Mr. Malty. I don’t think I’ve ever had a problem underpitching when using it.

tom_sawyer · November 11, 2011, 1:34am

I don’t measure volumes when I make a stater from a stored slurry. I just add about a cup to 2L and let it take off again. The viability of the yeast is going to vary depending on strain, storage conditions and other factors. I’ve used yeast stored 3 months and it takes right off in a starter. IF you really want to know cell count get a hemocytometer, some stain and a microscope. Otherwise, overpitching is better than underpitching.

conroe · November 11, 2011, 4:20am

Pitching healthy yeast into well aerated wort is far more important than pitching (0.75 million) X (milliliters of wort) X (degrees Plato of the wort).

560sdl · November 11, 2011, 12:17pm

And that is the best news I have heard all day! :cheers:

conroe · November 11, 2011, 2:39pm

Well a lot of brewers seem to think that’s some magical perfect number. It’s not.

560sdl · November 11, 2011, 2:47pm

Well, I can only count as high as the number of fingers and toes that I have, so “billions” is just inconceivable

a10t2 · November 11, 2011, 2:48pm

No, but it’s as good a starting point as any. If you don’t know how much yeast you’re pitching, you can’t adjust it in the future.

wahoo · November 11, 2011, 2:50pm

If your slurry is 7 weeks old you should definitely make a starter. I have seen 2 month old slurries that were totally dead. I’ve also seen ones that appeared to have perfect viability… it is hard to know.

tom_sawyer · November 11, 2011, 3:46pm

I agree about making a starter, even if its just a day to get it active again. On the other hand, I’ve never seen a 2 or 3 month-old starter not have decent viability and I’ve used over a dozen strains and have carried some of them for many generations.

conroe · November 11, 2011, 5:42pm

I’m not sure I was understood. I’m saying brewers should actually think about pitching rates. I haven’t read any of Fix’s books but that equation has not been in any of the that I have.

http://www.northernbrewer.com/documenta ... gRates.pdf

baratone_brewer · November 22, 2011, 12:45am

Methylene Blue staining is inaccurate once your viability begins to drop.

tom_sawyer · November 22, 2011, 12:53am

Its a heck of a lot more accurate than letting someone give you an educated guess and then compounding the uncertainty with a starter.

baratone_brewer · November 22, 2011, 10:26am

Maybe so, but Methylene blue staining is accurate only at viabilities above 90%. Even at that high of viability MB can over estimate by as much as 10-15% compared to plate counts.
If viabilities run below 90%, fluorescent dyes such as the magnesium salt of (Mg-ANS) are far superior to use for viability estimates. But, require a fluorescent microscope.