Accuracy of Yeast Calc for Old Vials & Freezing Potential
 

I made a 1.5l starter for a vial of WLP002 (best by Sep/4/2012, so production would be 5/4/2012) and sent it spinning on the stir plate. It took a full day to see some activity, but things came alive and bubbled along. When it was still again I stuck it in the fridge so I can decant and add 1.5l more wort.

When I use yeastcalc, it puts the viability on the vial at 10%, so all of the counts are super low. Is that really what I should expect? I was hoping to freeze some of the yeast before pitching next Monday, but will I be wasting my time?

No, it will be ok to freeze because you are taking the healthy yeast from the starter.

Will I really only end up with 79B viable cells after a 1.5L starter though (per yeastcalc I'm starting with only 10B viable out of the 100B original)? My concern is grabbing a bunch of dead cells along with the viable ones when I freeze. The numbers just seem low to me, but I'm no expert in this area.

The program calculates the starting viability of a yeast sample produced on a certain date in a preform, then shipped to the retailer and stored for various periods of time. If you step it into a starter the resultant yeast should be near 100% the day after the starter has finished out. The production date of the imput sample is not relevant, as you have used the starter process and high oxygen rates to propogate fresh colonies.

I can't say if 10% is accurate. I've done no tests on my own. But everyone seems to trust the calculators, so they are considered fairly accurate. But, tt's very dependent on how the yeast was stored. If conditions were perfect you may be well above the 10%. If conditions were not so good, that may be about all you have.

If the concern is freezing dead cells, remember they floc very quickly. Once you are ready to harvest, let the starter sit for 10-15 minutes and all the dead cells should fall out. You can then pour off the yeast and liquid on top of the sludge layer (it will be very small). What you now have is very viable yeast.

For his concern, the production date is relevant. Based on the calculator, he has 90 billion dead cells floating around in his starter. Moving them to a slant or glycerin suspension would be a waste.

Exactly my point. I'm trying to see if anyone has taken a look at a 4 month vial under a scope to see if it really is anywhere near 10% viability. I'd step up the starter a few more times if I needed to, but I also don't want to severly overpitch if I grow up to 10x more than I need (assuming that the viability in the tube was anywhere between 10% and 100%).

The vial was stored in the fridge for the entire time, except for a 30 minute drive from the store back home in an air-conditioned car. I just waited too long to use it before I realized it was at the expiration.

The only way I can come up with to tell is to measure the volume of the slurry you make.

If you start with a vial with 15 mL of settled yeast, then grow up a starter let the entire thing compact, and have 30 mL you can be certain that you have at least 15 mL of good stuff.

If you let that same starter settle for a few minutes, then decant and let that compact, you can be sure nearly all of it is good.

You have to make a judgement call on how much of the original stuff you think is still active. The guys that made the yeast calculators did look at them under a scope. They did the counts, they made calculators. All 3 folks that have done it have come up with nearly the same formula, so it's probably pretty accurate.

Which three guys? I am currently comparing yeast calc to mr.malty. I put in a dat of 11/18/2012. Yeastcalc gives me 60% viability and Mr.Malty gives me 30%.

So I made a 1.5 L starter for a 1.041 OG beer. According to Mr.Malty I am right on with my counts but according to Yeastcalc I overpitched by 60 billion cells (or about 36%).