Yeast harvesting, how much is enough?

[Anderson_NJ]

So I've been looking into harvesting my yeast for future homebrews. I tend to like brewing big beers, and therefore my pitch rate is of particular concern. My question is this: when harvesting yeast from my primary, and then proceed to make a starter (maybe even build it up), how do I know I have enough yeast to meet the proper pitching rate?

 

[flars]

Pour your yeast, from the fermentor, into a container that has volume markings. Some quart canning jars have volume graduations for ounces and milliliters. Let the yeast settle out from the beer for a day or two and you will have rough idea of how much yeast you have.
I can usually get 375 to 400 ml of yeast form an average gravity brew.

 

[Anderson_NJ]

But how do you know how much is enough? Are there so many yeast cells per ml of yeast slurry?

 

[solbes]

I am a little less scientific in this area, but I think over pitching is much less of a concern than under pitching. I'm sure in almost all cases I am closer to over pitching than under. Its true you can approximate slurry volume, but how much of that slurry is trub, how many are active yeast cells, how many are dead yeast cells? I have no idea, so I just try to keep it simple.

- Ahead of time I sanitize 0.5 or 1 qt Mason jars. 2 jars per beer batch. Add filtered water to half full mark, boil in microwave, loosely cover, and place in fridge until cold
- Sanitize a 1 cup measuring cup
- For 1.050 and below brews, I take 1 cup of slurry from the top of yeast/trub in primary. For 1.050-1.080 I take 2 cups of slurry. For 1.080+ I will take anywhere between half and 2/3 of the yeast/trub cake depending on beer size.
- Add this to sanitized jars, swirl, and set timer for 15 minutes.
- Pour off top of mason jar into second mason jar until it is either filled, or starts to get to the clumpy trub layer I want to discard.
- Place 2nd jar into fridge. I keep these for up to 4 weeks (direct pitch within 4 weeks), after which I would require a starter prior to pitching. I always decant most of the liquid on top prior to pitching.

 

[flars]

But how do you know how much is enough? Are there so many yeast cells per ml of yeast slurry?

According to WoodlandBrew, there are 2 billion yeast cells per milliliter. The link to post https://www.homebrewtalk.com/f163/saving-yeast-how-much-save-512185/#post6633057
More information on his site about yeast harvesting and yeast viability.

 

[WoodlandBrew]

Thanks flars,

Yes, 2 billion per ml of settled slurry is normally pretty close. It can be closer to 1B/ml if there is a lot of trub, or 3-5B/ml if the yeast is exceptionally clean (such as directly from the manufacturer)

This is also about what Kara Taylor of White Labs estimates. See "Yeast Handling and Technology"