Pitching rate with harvested commercial yeast

[Bradmont]

I harvested some yeast from a bottle of Unibroue La Terrible that I want to use for a Trois Pistoles clone, and am trying to figure out the right pitching rate. Since I started with a small harvested sample from the bottle of a 750ml bottle and gradually stepped it up, I'm wondering if the pitching rate will be the same or are assumptions different when starting with a larger number of cells like in a smack pack?

Using brewtarget to calculate, it told me that with:
2.5 gal @ 1.093, 1.035 starter OG, .75 cells/(ml*P) = 158 billion cells needed, or 3 cup starter. My last step up in the yeast was to a 750ml jar (3 cup); will this be enough?

Also, I grew the yeast a couple weeks ago and it's been sitting in my fridge; I'm wondering whether decanting and pitching a bit of low gravity wort before brewing is necessary or should it be ok without?

Thanks!

 

[thesanch]

The final cell count of a starter is determined by the inoculation rate and the starter size. You'd have to estimate how many cells you started with before the final step to determine how many cells you ended up with.

This blog post explains it pretty well:
http://www.beersmith.com/blog/2011/01/10/yeast-starters-for-home-brewing-beer-part-2/

 

[fuhmon]

Also, I grew the yeast a couple weeks ago and it's been sitting in my fridge; I'm wondering whether decanting and pitching a bit of low gravity wort before brewing is necessary or should it be ok without?

Thanks!

i would feed it fresh wort morning of brew day.

 

[Bradmont]

Thanks guys. thesnatch, I really have no way of estimating my starting number of cells... I started with maybe a tbsp of beer from the bottom of a 3/4l bottle, and stepped it up by doubling the volume several times. Do you know of a way I could estimate cell count, say by measuring the volume of the yeast cake?

 

[thesanch]

Take a look here:
http://www.mrmalty.com/calc/repitch.html

That should estimate about how many cells you have in your slurry...

Also, just a quick note, doubling the volume each time does not double the number of cells.