[RPIScotty]

Looking for some basic information on repitching yeast.

I'm looking to grab a small cube mini-fridge for use a yeast "archive". When dealing with the yeast from a recently fermented batch of beer, what can one expect as far as cell counts for the slurry? What is the best way to use this yeast, immediately re-pitched or store and used in a starter later?


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[a10t2]

For what you'd scoop or dump from a fermenter, most likely 1-2 billion/mL. It's really helpful to do a few counts with a given strain, after which you can probably get away with eyeballing it.

You always want to re-pitch as soon as possible. I don't have any problems with storing slurry for a couple weeks under beer, though. After that I'd take a small quantity and grow it back up.

[S. cerevisiae]

Sean's advice is on the money cell count-wise and storage-wise.  Slurry is a temporary means of storage.  The easiest, most compact, and most foolproof way to store yeast for more than a month or two is on slant.  Now, if you can afford to operate a -80C freezer, cryostorage is the way to go.   I own quite a few expensive cultures, but I cannot justify the cost of a -80C freezer.

[RPIScotty]

I'll have to do a quick search and find your slant thread. I remember seeing it at some point before I was using liquid yeast.


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[evil_morty]

You can get a decent estimate if you let the yeast fully compact in a mason jar (or something similar).  I'd have to go find the cells/mL estimate that's out there but it should be a better estimate than you could get with fresh slurry.

[RPIScotty]

You can get a decent estimate if you let the yeast fully compact in a mason jar (or something similar).  I'd have to go find the cells/mL estimate that's out there but it should be a better estimate than you could get with fresh slurry.

Can you clarify your statement? I'm not sure I follow the logic here.

[S. cerevisiae]

There are two basic types of slurry, thin slurry and thick slurry.   I believe EM is calling thin slurry "fresh slurry."  Thin slurry is what one gets if one resuspends the solids before taking one's crop.  Thin slurry will settle into thick slurry and supernatant (the clear liquid that lies above the solids).  Thick slurry usually contains between 1 and 2 billion cells per milliliter.  Wyeast recommends using 1.2 billion as the number of cells per milliliter when making a pitching estimate.

I shoot for a pitching rate of between 3 and 10 billion cells per liter depending on what I want to achieve out of a batch of non-high gravity wort. Your batches are so tiny that you are looking at anywhere between 11.4 and 38 billion cells, which equates to 11.4 / 1.2 = 9.5 and 38 / 1.2 = ~32ml of thick slurry.

[evil_morty]

There are two basic types of slurry, thin slurry and thick slurry.   I believe EM is calling thin slurry "fresh slurry."  Thin slurry is what one gets if one resuspends the solids before taking one's crop.  Thin slurry will settle into thick slurry and supernatant (the clear liquid that lies above the solids).  Thick slurry usually contains between 1 and 2 billion cells per milliliter.  Wyeast recommends using 1.2 billion as the number of cells per milliliter when making a pitching estimate.

I shoot for a pitching rate of between 3 and 10 billion cells per liter depending on what I want to achieve out of a batch of non-high gravity wort. Your batches are so tiny that you are looking at anywhere between 11.4 and 38 billion cells, which equates to 11.4 / 1.2 = 9.5 and 38 / 1.2 = ~32ml of thick slurry.

that is what I'm referring to.  the other thing about letting the slurry compact is you can kind of see distinct layers of yeast and trub which helps to get a more accurate estimate.  really though with the way you guys are operating in terms of pitching rates it seems like you care much more about vitality than number of cells.  if I was operating with that mindset I wouldn't worry to much about this.

[a10t2]

You can get a decent estimate if you let the yeast fully compact in a mason jar (or something similar).  I'd have to go find the cells/mL estimate that's out there but it should be a better estimate than you could get with fresh slurry.

Can you clarify your statement? I'm not sure I follow the logic here.

If you really let the slurry compact out (i.e. a week stored just above freezing), it'll settle in at more like 3-4 billion/mL. You could then harvest that and get a more precise pitching rate due to a more accurate estimate of cell count. You could also resuspend it in known volumes of beer or water to get a little intuition for what slurries of varying thicknesses look like, in lieu of cell counts.

[S. cerevisiae]

If you really let the slurry compact out (i.e. a week stored just above freezing), it'll settle in at more like 3-4 billion/mL. You could then harvest that and get a more precise pitching rate due to a more accurate estimate of cell count. You could also resuspend it in known volumes of beer or water to get a little intuition for what slurries of varying thicknesses look like, in lieu of cell counts.

Three billion plus cells per milliliter is pure yeast.  Most crops are yeast, break, and other organic matter.

[a10t2]

Three billion plus cells per milliliter is pure yeast.  Most crops are yeast, break, and other organic matter.

Good point, that does assume a nice clean sample without any significant "heads or tails".