How do you know how much yeast you have

[AColdOneInNH]

With the great posts on this site I harvested yeast for the first time on 1/23 and plan to use that yeast for a cream ale (OG 1.040) on Friday. There was a nice 1/4" of yeast in the mason jar that's been in the fridge since I harvested.

I made my first starter today using around 650ml of water and a 1/2 cup of DME. When I added the yeast to my starter (after boiling and cooling), I dumped out most of the water above the yeast so I added a pretty thick solution of slurry. I have this on a stir plate now.

So, after looking at mrmalty.com and yestcalc.com, I'm not sure how to tell if I'll have enough yeast. Yeastcalc requires the initial cell count of your yeast, and I have no idea what the count was of my slurry. Mrmalty has the Repitching from Slurry tab, but how do you know what to pick for yeast concentration and the non-yeast percentage? Do you just take a guess and hope you're right?

 

[Kaiser]

Do you just take a guess and hope you're right?

yes that's what you have to do. At least you can make an educated guess if you know the weight or volume of the yeast. I found settled slurry densities to be between 2 and 4 Billion cells per gram. I know that's a big spread. There are strain dependent differences and there is a difference between washed or freshly propagated and non-washed yeast.

I'd assume 3 Billion per gram and go from there.

If you want to have yet another yeast calculator, check out Brewer's Friend (http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/) it uses a yeast growth model that I proposed as default. But It may confuse you even more since it does not give you the same results as YeastCalc or MrMalty

Kai

 

[AColdOneInNH]

If you want to have yet another yeast calculator, check out Brewer's Friend (http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/) it uses a yeast growth model that I proposed as default. But It may confuse you even more since it does not give you the same results as YeastCalc or MrMalty

Thanks, Kai. On the contrary, having a third calculator is great. As long as one of them comes close to telling me I have enough yeast, I'll sleep fine. I don't have any crazy need to verify the results of each calculator. (Ok, that's a lie. I can't really turn off the engineer in me, so I find myself using a calculator to understand how the online tools get their numbers. I haven't slept in days...)

In this case, with a 1.040 beer, I expect I'll be fine as long as the yeast is viable.