How many cells in a fl.oz. of yeast?

[petrolSpice]

I've started to harvest yeast from the fermentation blowoff. I use a sanitized half-gallon mason jar to catch the liquid from the blowoff. Then I usually "wash" the yeast and store it in the fridge in a mason jar. Of course after a few says the yeast settles to the bottom of the jar and I can read the volume of yeast I have.

On my last brew I caught around 4 fl.oz. of yeast. I have no idea how many cells this is. Any ideas?

I can try to compare it to a "vial" of White Labs liquid yeast which is supposed to be around 100 billion cells, but I don't know how much volume is in a vial.

2 brews ago I made a 2L starter from around 2 fl.oz. of harvested yeast. The fermentation was explosive. It started blowing off within 6 hours and continued to do so for 3 days, OG 1.071. So part of me thinks I pitched WAY too much yeast.

 

[jerbrew]

Honestly, it's hard to pitch too much yeast especially WAY too much yeast on a 1.071 beer. Unless of course that's a one gallon batch but i doubt it. Or you're repitching onto a monster yeast cake. Everything i've experienced and have read indicates hat you really just need a lot of healthy yeast cells. You can probably find a decent answer to your question but if you're getting a healthy 2 L starter you're good.

The only exception to being hard to pitch too much yeast would be a hef. IN which case your goal is usually to underpitch in order to coax those stressed ester byproducts.

 

[rhys333]

Its easier to look at it with the metric system, but you can safely estimate 1 to 1.5 billion cells per ml of slurry with about 15% cell loss per month of storage. That would be about 30 to 45 billion cells per fl.oz. Check out the Simple Yeast Storage Procedures thread in the yeast section for more info. Good news is you don't need to wash (rinse) your yeast either, just collect and refrigerate.

 

[petrolSpice]

This link says "The average 50-milliliter smack pack of yeast has roughly 2.5 billion to 4 billion cells once it has reached high kraeusen (the peak of fermentation)"

That comes out to 0.05-0.08 billion cells per mL... why does that not sound right. So to reach 100 billion cells I'd have to pitch 25-40 packs?

https://byo.com/color/item/1248-pitching-by-numbers

 

[rhys333]

This link says "The average 50-milliliter smack pack of yeast has roughly 2.5 billion to 4 billion cells once it has reached high kraeusen (the peak of fermentation)"

That comes out to 0.05-0.08 billion cells per mL... why does that not sound right. So to reach 100 billion cells I'd have to pitch 25-40 packs?

https://byo.com/color/item/1248-pitching-by-numbers

1998 though - That's some old data right there. The smack-packs now are rated at 100 billion cells. You basically want to double it to 200B for an average 5 gal 1.050 batch of beer. As for harvested slurry, 1/4 pint of the stuff is sufficient as long as its fresh(ish).

 

[petrolSpice]

Just looked again and I collected about 7 oz of compacted yeast from the last brew.

Is it safe to say that this is probably too much for a 5 gallon batch?

 

[rhys333]

Just looked again and I collected about 7 oz of compacted yeast from the last brew.

Is it safe to say that this is probably too much for a 5 gallon batch?

5 ounces of that will probably do it (as long as its relatively fresh).

 

[petrolSpice]

5 ounces of that will probably do it (as long as its relatively fresh).

It's pretty fresh, caught it 8 days ago and its been in the fridge for 5 of those days.

 

[rhys333]

It's pretty fresh, caught it 8 days ago and its been in the fridge for 5 of those days.

You're good there and safe to pitch most or all of the jar. If you crack it and bubbles start up quickly, then its a good sign you have really active yeast. Let it warm up before pitching too if you can.