Author Topic: Measuring for Repitching  (Read 874 times)

Offline mmitchem

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Measuring for Repitching
« on: November 26, 2012, 12:18:42 PM »
Greetings All,

I have always used a fresh vial yeast starter for brewing. After a few years of buying countless vials I would love to start washing and repitching yeast.

I understand the basics of harvesting and don't really think the washing/collecting will be a challenge. My problem is calculating how much of that yeast to pitch.

I would still like to utilize a starter if nothing more than to introduce the yeast to fresh wort before pitch to get those little guys back into the swing of things. I see Mr. Malty has a great repitch feature and Kai has given me the skinny on viable cells per gram. How much of the slurry is non-yeast? Would it be good to mark my mason jars in mL to know how much is in each jar? My concern is that I do not want to underpitch and I do not want to be wasteful at the same time. Any pointers or practices that folks use to get the yeast count in the good zone?

Thanks in advance!!
Michael P Mitchem
Beer and Ale Research Foundation (B.A.R.F.)
AHA Member since 2011

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Re: Measuring for Repitching
« Reply #1 on: November 26, 2012, 12:31:50 PM »
There is substantial variability in the cell density in slurries and I believe it also depends on how much trub you allow in the fermenter. Not all yeast washes equally well. If I would be pressed for a universal number I would assume 2.5 Billion cells per gram (roughly same as ml) in a dense slurry that was harvested from a primary.

Other than that I don't have enough samples across various yeast types to be less general. Maybe over time I'll see a pattern. In practice I have seen the density of well set slurries rage from 2 to 4 B/g. Loose slurries, as you get with poor flocculators will have less cells.

Kai

Offline mmitchem

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Re: Measuring for Repitching
« Reply #2 on: November 26, 2012, 12:40:05 PM »
Thanks Kai. That leads me to another question. Say I am washing yeast from the slurry that was collected from a cold-crashed, well settled primary fermentation. If I wash yeast from a cake, store it in the fridge and get it cold and settled again, would the slurry in the mason jar be considered a dense slurry that could be measured in g or mL? Of course the estimate at this point would be measured at 2.5B/g. 
Michael P Mitchem
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Re: Measuring for Repitching
« Reply #3 on: November 26, 2012, 01:40:12 PM »
It depends on the yeast how dense it will be. I plan to take pictures that illustrate the density of a slurry and then report the cell count per gram that the slurry had. But I haven't started yet on that.

If the sediment stays in place when you tilt the jar, I would call that dense.

Kai

Offline mmitchem

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Re: Measuring for Repitching
« Reply #4 on: November 26, 2012, 01:58:01 PM »
I am going off of information that you had previously given me where you would guess that WLP833 could be estimated the roughly the same as WLP830 at 2.5B/g. WLP833 is my favorite lager yeast by far and would love to harvest this yeast to offset the cost of a fresh purchase every brewday. I have a Munich Dunkel fermenting currently and plan on using this as my first harvest. The fermentation is going very well so it is a great candidate.

I can relate to the slurry not moving freely as being what you would consider a dense slurry. That is really fantastic information that will serve me well for sure.

Microscopy is the next step in this process, but that will have to wait for now.

One more question regarding the yeast harvested from your primary. Does the viability decrease in the same manner as it would for a vial bought at my LHBS?
Michael P Mitchem
Beer and Ale Research Foundation (B.A.R.F.)
AHA Member since 2011

Offline dimik

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Re: Measuring for Repitching
« Reply #5 on: November 26, 2012, 09:53:50 PM »
One more question regarding the yeast harvested from your primary. Does the viability decrease in the same manner as it would for a vial bought at my LHBS?

As far as I know, yes. I've seen data showing that viability levels off at something like 60% after a couple months and then goes down slower, but I can't remember where...
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