How much slurry to pitch into a RIS?

[CascadesBrewer]

Today I harvested some yeast slurry from a porter brewed with Safale S-04 (pic below). Tomorrow I am thinking about brewing a 2.5 gal batch of a Russian Imperial Stout. The beer should be right around 1.100 and 10% ABV.

So how much of my yeast slurry should I pitch?

Looking at the Mrmalty calc it say I need 199 Billion yeast cells. I have no clue where to set the Yeast Concentration and Non-Yeast Percentage values, but with the default values it says I need 97 ml (3.3 oz). If I bump the Non-Yeast value to the max of 25%, it says 106 ml (3.6 oz).

Looking at the stickied post about yeast storage and using the "normal" value of 1.5 billion per ml, I guess I need 132 ml (so 4.5 oz).

So should I pitch somewhere around 4 oz of my slurry? Is it better to pitch a little more, say 6 to 8 oz? Is it better to pitch the entire 16 oz jar slurry? I am planning about 2.6 gal into a 5 gal carboy, so I should have good headspace for a strong fermentation (knock on wood).

Pic of pint size slurry jars:

 

[LLBeanJ]

I would go to the high side and pitch at least 8 oz, maybe even 12. An OG that high is going to stress the yeast, so more is definitely better in this case. Pitching an entire pint would be fine, too.

 

[CascadesBrewer]

I would go to the high side and pitch at least 8 oz, maybe even 12. An OG that high is going to stress the yeast, so more is definitely better in this case. Pitching an entire pint would be fine, too.

Thanks. I was thinking I would pitch one jar and I was hoping it would be enough, so I was a little surprised to see calcs in the 4 oz range.

Thinking about it...I have fermented directly on top of the yeast cake from a previous batch...and 1 of these jars is maybe 20% of the yeast cake that was there (from a 5 gal batch). I have harvested yeast before where I washed the yeast. In that case I would pitch the entire "pint" of cleaned yeast into a batch of regular strength beer (there was 1-2" layer of yeasty stuff).

It is hard to find info on over pitching other than people saying "it is really hard to over pitch at the homebrew level".

I guess I never played around with calculating yeast pitch rates before...just either pitched a 16 oz starter from liquid yeast or pitched a dry yeast pack.

 

[Sadu]

Best one of these I have ever made was where I pitched 3 pints of super fresh slurry into 6 gallons wort. If you have the yeast, pitch a pint or so.

 

[CascadesBrewer]

Thanks...got 2.5 gal of 1.104 beer in the fermenter and pitched one pint of the slurry. Crossing my fingers!

P.S. WOW this wort is dark and sweet...it is based off a clone of Great Lakes Blackout Stout.

 

[CascadesBrewer]

Maybe 6 hours of so after pitching I have some pretty healthy looking yeast action and airlock activity!

I ferment in the basement and the cold air and cool tile floor usually keeps my ales in the 65F to 68F range. I was a little worried about this one so I put it in a water bath with cool water where I can add ice to keep it in check and add a little thermal mass...also the temp strip that is on the carboy is above the wort line anyway so figured my dial thermometer in the water would work.