"Waking up" a washed yeast slurry

Let's say I have 300ml yeast slurry that is about 6 weeks old. In general I think this is thought to be a bit out of the optimal range to just pitch directly. Let's also say that mrmalty says I need about that much for a big beer I want to brew. How large of a starter would I need to make to get it ready for pitching?

Just do a 2L starter, decant, swirl, and pitch it. Unless it's a double digit ABV brew, 2L is enough.

How big is big?

rhamilton said:

Just do a 2L starter, decant, swirl, and pitch it. Unless it's a double digit ABV brew, 2L is enough.

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This is what I would do. Depending on how big you mean by "big," you may be able to get away with 1.5L. I tend to err on the side of too much yeast, so I would probably stick with 2L.

Yankeehillbrewer said:

How big is big?

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1.080. Mrmalty includes adjustment for viability so the 300 ml is supposed to have the right amount of viable yeast. The issue is that they may be dormant. Do you really need a large starter? Would 500ml or 1L not do the trick for getting them active?

EllisTX said:

1.080. Mrmalty includes adjustment for viability so the 300 ml is supposed to have the right amount of viable yeast. The issue is that they may be dormant. Do you really need a large starter? Would 500ml or 1L not do the trick for getting them active?

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Well without knowing your cell count / ml - it's pretty much impossible to get a true answer which you are looking for. Now the yeast will be active @ 500ml/1L but your count will be lower vs a 2L starter.

And another factor is viability -- MrM assumes 97% viability -- I can tell you it'll be alot lower in a 6 month old slurry.

I prefer this; http://www.yeastcalc.com/index.html, because you can enter cell count and production date and it will figure that out for you. So in your case enter 300 under "Initial Cell Count" then put the date you washed it as "Production Date" and it will push you in the right direction..

EDIT, I thought you wrote 300 billion cells, but you put ml. You can figure that out too though. I'll try to find the link I have for that..

OK, this is what I found. I know it's just an approximation, but it gives a basis to go by..
Originally Posted by http://www.wyeastlab.com/com-yeast-harvest.cfm
Estimates of cell counts can be made using percent yeast solids of the slurry. Percentage of yeast solids per volume of slurry can be estimated by allowing a sample to sediment under refrigeration and estimating the percent solids. Generally 40-60% yeast solids will correlate to 1.2 billion cells per ml

Thanks Stauffbier. Mrmalty calculates all that you were refering too. Viability from date, % solids, etc. I understand how to estimate the amount of healthy yeast that a certain volume should be. Listening to podcasts with Jamil and Palmer, they say that after a certain time after harvesting that you should wake the yeast up with a starter. Since increasing the cell count isnt what you would be going for in this instance, would just a small starter not be successful?

So according to Mr.Malty a 6 week old slurry is only about 30% viable. Using that along with the estimate of 1.2 Billion cells per mL, I figure you have about 120 billion good cells, which would equate to about 3 vials of new yeast. Mr.Malty says you need 287 Billion for that size beer in a 5.5 gallon batch, and that it would require a 1.8L starter with 3 vials to get to that number.

EllisTX said:

Since increasing the cell count isnt what you would be going for in this instance, would just a small starter not be successful?

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I will wake up a yeast starter that I just made 2 or 3 days prior with a 1 cup starter on brew day, but in your case according to YeastCalc your 6 week old 300 ml of yeast would only give you about 245 billion cells. It says that for a 5 gallon batch at 1.080 you would need to pitch 275 billion cells. I would make a 1L starter with the 300 ml that you have to build up a little bit more if it was me..

If you trust your handling procedures, just straight pitch it. Think about it, you could just straight pitch several vials of yeast, you don't have to 'wake' it up. Once it is in the wort, it will know what to do.

If you have any issues with your yeast or handling, then make a standard 2L starter.

I don't trust Mr. Malty viability figures, I believe yeast slurry stays much more viable that it predicts.