Let's clarify: 1 B/mL or 2.5 B/mL or ???

[TheLadybugTree]

From my poking around in the last month I have come across a seemingly unspoken inconsistency. Depending which pitch rate calculator you use, the resulting size of starter or amount of slurry drastically differs.

Mr. Malty:
http://www.mrmalty.com/calc/calc.html
Default yeast concentration of slurry: 2.5 B/mL (ish)

Brewer's Friend:
http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/
Default yeast concentration of slurry: 1 B/mL (ish)

Both are great tools. Both give you the option to edit the setting of yeast concentration. But they have different defaults. It has a profound effect on pitch rate. I am currently planning my yeast for a milk stout and also an IIPA. With one calculation I can pitch straight slurry, with the other I need a starter. Granted, amount type of yeast, hardness of deposit, etc. plays a part in deciding this.

Can you guys 'pitch' in your ideas on yeast concentration? How do you gauge the concentration? I have been using 2.5 lately because I read something a long while back that has me believing it is a safe bet. Then I saw this:

http://beermusing.com/joomla/77-nhc...sheff-heretic-brewing-and-the-brewing-network

"Benchmarks for visually estimating concentration of yeast cells:
3 billion cells per ml – White Labs yeast vial, after shaking
8 billion cells per ml – White Labs yeast vial, before shaking
1 million cells per ml – 13 x 100 ml test tube, threshold between clear and slightly cloudy mass of 100 billion cells (clean, no water) is about 8 grams"

I am sure my cold crashed washed yeast is not as pure as White Labs. But it would definitely be similar in density. Maybe not 8 B, but certainly more dense than a shaked vial. What am I missing here? Can we have a good discussion about how to estimate the yeast concentration of a washed (rinsed) yeast cake? Pictures are helpful too if you can.

Here are my jars of s-05 washed yesterday and sitting in fridge over night:

About 200 mL of dense slurry in there. Yeast concentration will make a HUGE difference:

8 B/mL: 1600 (only need 1/4 of it)
2.5 B/mL: 500 billion cells (perfect pitch rate)
1B/mL: 200 billion cells (need starter)

What do you think?

 

[boydster]

I may be wrong, but I recall reading somewhere that if you initially pitch somewhere between .75 million and 1 million cells/ml/°P, the number of yeast cells should increase 4- to 5-fold. If you save the entire yeast cake, you have all of those cells divided across however many jars. I've used that general guideline and it's served me well for estimating how much slurry to pitch.

Once you go down the yeast rinsing road, you end up tossing out a lot of those, but I don't know of a way to estimate how many, and that brings us around to making a really crude estimate about what is actually left unless you have the equipment to do a cell count.