How much slurry do YOU pitch?

This will be my first time re-pitching slurry. I was looking on mrmalty.com, and there are a couple of little sliders (like the thickness of slurry and concentration of yeast) that I'm blindly guessing at and change the amount to pitch significantly.

I'm making a session IPA, so fairly low OG. I've got two large mason jars of slurry. I'm at work right now and forgot the actual volume of each. I know I'm overthinking this, but I don't have the patience to sort and count out 237 billion live yeast cells. So, those of you who repitch slurry (and do so without too much overthinking), what is your rule of thumb for the amount of slurry?

If its washed yeast and has been in the fridge a few days, I estimate about 3 billion cells per mL, less if there is a lot of trub. So if there is 50mL of tight yeast, thats about 150 Billion cells. If its clean yeast, I estimate 4 billion per mL. Just remember that its better to pitch a little more than not enough. Gathering yeast slurries will result in a lot of yeast so just dont pitch all of it.

I do three gallon batches and recently just did my first slurry repitch. I think it was a few table spoons. Fermentation went off as normal.

For direct pitch right from the fermenter, lately I've been going with 1ml slurry = 1 billion cells and I've had good results.

Thanks for the replies. It's hard for me to wrap my head around something that has online calculators and precise cell counts, yet is so arbitrary.

I'm assuming my slurry is pretty "dirty", so I'm thinking 250ml will get my cell count about between 200 and 250, which is where Mr Malty says it should be for my beer. Just so I'm clear on the consequences, If I overpitch, worst case it that I have a super active fermentation causing a messy exploding fermenter, and underpitching could cause of flavors. Is that about right?

notyal said:

Thanks for the replies. It's hard for me to wrap my head around something that has online calculators and precise cell counts, yet is so arbitrary.

I'm assuming my slurry is pretty "dirty", so I'm thinking 250ml will get my cell count about between 200 and 250, which is where Mr Malty says it should be for my beer. Just so I'm clear on the consequences, If I overpitch, worst case it that I have a super active fermentation causing a messy exploding fermenter, and underpitching could cause of flavors. Is that about right?

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Basically. Underpitching isnt always bad, but its just a rule of thumb to avoid it if possible. Even if you only have 200 billion cells, that should be plenty for your next beer.

When you first open the repitching from slurry tab, those sliders are set somewhere. The slurry thickness is a good figure as preset for harvested slurry that's been in the fridge overnight. ie moderately compacted, but not super super tight like you'd find in the bottom of a White Labs vial. So I tend to leave that as is. If you're storing yeast for an extended period in the fridge, then it'd be thicker than that (but also less viable). If you're just going based on what settles out during harvest but without some fridge time to crash it, then thinner than that. But if my understanding is correct, that's why he has it set where it is.

And then if you see any non-yeast in your slurry at the bottom, I'd just assume 25% to be safe. That's what I do.

And then I just use his figures, and then either increase or reduce the amount proportionately if I want to adjust pitch rate from there.

For 5g batches, I typically will pitch about 1/2 - 3/4 cup of slurry. If it is sad yeast, it sinks to the bottom. Typically, this is enough for me to get a very good start. BTW, not all yeast is equal. If you are doing heffs or german ales, you really should top crop. I have had nothing but terrible luck with lagers so I always use fresh and healthy lagers. My rule is 2 packets for anything under 60 GP and 3 packets for anything over. Of course, I also don't use liquid yeasts for lagers either so it is fairly cheap.