Author Topic: What volume of washed yeast to pitch into 5 galon brew?  (Read 820 times)

Offline MarkWebb

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What volume of washed yeast to pitch into 5 galon brew?
« on: September 09, 2018, 12:54:30 AM »
I have watch a few YouTube's on yeast washing. They end with yeast cakes in mason jars. I'm interested in the next step i.e. how much of the washed yeast cake to put into your next 5 gallon brew. How does one calculate this?
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Mark

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Re: What volume of washed yeast to pitch into 5 galon brew?
« Reply #1 on: September 09, 2018, 06:00:37 AM »
Always a fun task.

I used several parameters for figuring the amount of rinsed slurry to pitch into a batch.  You need to look at the density, color, and cleanliness of the yeast.  If I see a some trub left in the yeast, I will apply a percentage factor based upon how much of the yeast cake is yeast cells vs trub.  I also add a color factor based upon the color of the yeast slurry.  If the yeast is not bright white or off-white, I discount the amount of viable cells further. 

Then I figure that a compacted yeast cake generally contains around 4.5 billion cells per ml.  I then apply a factor for how dense the yeast cake is, if it is not compacted, and then the factors I outlined above.  This will give me an approximation of how many cells per ml of slurry I have and I divide the number of cells I need for the recipe by that number to give me the ml of slurry to pitch.

It takes some time and experience to figure this all out, and don't be too afraid of over pitching a bit to be on the safe side. Realize that there is a pretty wide window of yeast cell counts that will work just fine.  Generally, the higher the gravity of the recipe I am pitching into, the more I 'underestimate' my slurry cell count leading to a slightly higher pitching rate.

The last few years, I have started doing actual cell counts and confirmed my educated guesses outlined above as being OK. 
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Offline grommetik

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Re: What volume of washed yeast to pitch into 5 galon brew?
« Reply #2 on: November 09, 2018, 02:29:25 PM »

... figuring the amount of rinsed slurry to pitch ... 
... I also add a color factor based upon the color of the yeast slurry ...
... I then apply a factor for how dense the yeast cake is ...


1. I'm guessing "rinsed slurry" is your term for "washed yeast"?
2. What is your color factor? Do you have a scale?
3. How do you determine yeast cake density?

Thank you,
Mark

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Re: What volume of washed yeast to pitch into 5 galon brew?
« Reply #3 on: November 09, 2018, 06:24:03 PM »

... figuring the amount of rinsed slurry to pitch ... 
... I also add a color factor based upon the color of the yeast slurry ...
... I then apply a factor for how dense the yeast cake is ...


1. I'm guessing "rinsed slurry" is your term for "washed yeast"?
2. What is your color factor? Do you have a scale?
3. How do you determine yeast cake density?

Thank you,
Mark

1.  No, I use the term 'rinsed slurry' for a good reason.  I have rinsed the yeast of most of the trub.  'Washed yeast' has a whole different meaning -- that the yeast has been rinsed with acidified water to kill or retard any contaminant bacteria which cannot tolerate the acidic conditions.  Too often we home brewers get lazy with the definitions, myself included.  I prefer to just rinse the yeast with sterilized water as, while it is not difficult to acid wash the yeast, it takes a toll on the viability and cell quality.


2.  Pure yeast cake is slightly off-white to cream colored.  Much depends upon the strain of yeast.  As the yeast gets old or is contaminated with trub, the color starts to go towards straw then tan colored.  If the yeast cake is brown, toss it or you can try to make a starter as most of the yeast is dead or dying.


3.  Pretty much by consistency.  The old White Labs yeast vials were a good calibration tool for this as the level of the thick yeast paste on the bottom (before you shake it up and re disperse the cake) is about 100 billion cells.  The volume was around 25 to 30 ml of yeast cake if you carefully decanted the thin fluid from the top.  Harder to quantify with their new packaging.  Compacted yeast will be like a clay mud, almost hard to scoop out and be about 3.5 to 4 billion cells per ml.  If the slurry has some flow to it, the cell count is much less.  It is sort of hard to describe as most of this is experiential based combined with cell counting.  These days I take it down only to a thin slurry and end up with about 1.5 to 2 billion cells per ml which makes it easier to measure out the correct volume to pitch.

In general, you can over pitch quite a bit before you toss in too much and inhibit the yeast character in the resultant beer, so don't be afraid to toss in a little extra slurry. 
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