White labs Irish ale - past prime

[liamw]

Hi all,

I've got a vial of wl Irish ale liquid yeast. It's use by date was September 23rd or so. I was planning on using it in an Irish red that I'm making (1.050 or so og). If I make a 2 litre starter with this would I be ok? Or am I better off tossing it and using some s-04?

Thanks

 

[flars]

You are much better off using a starter pitch rate calculator than just guessing.

Starter/pitch rate calculators use the production date of the yeast to determine viable yeast cells available and starter size to get to the pitch rate for the estimated OG of the wort.
http://www.brewersfriend.com/yeast-pitch-rate-and-starter-calculator/
http://www.homebrewdad.com/yeast_calculator.php

 

[liamw]

When I type in the manufactured date, may 23/14 (4 months prior to use by date as per instructions), I get quite a range of viability. Brewers friend gives me 0%, mrmalty gives 10% and yeastcalc gives 20%. In your experience, what do you find to be most accurate?

 

[flars]

With yeast that old I will go with 10%, make a 1.010, 1 liter starter. With old yeast a weak starter is recommended to reduce yeast cell wall stress.

Give the old yeast extra time, stir plate or shake and swirl. Estimate the end yeast volume for at least a growth rate better than 1.0. Step up to a 1.040 starter if the yeast did seem to propagate new cells.

 

[liamw]

Thanks so much for your help, I'll follow your advice.

One question though, just for my own curiosity, why do the calculators not take into account the o.g. Of the starter? I get the same growth whether or not I use a starter of 1.010 or 1.040, as per the calculators.

 

[flars]

Thanks so much for your help, I'll follow your advice.

One question though, just for my own curiosity, why do the calculators not take into account the o.g. Of the starter? I get the same growth whether or not I use a starter of 1.010 or 1.040, as per the calculators.

I think it is just a peculiarity of how the software was built. Yeast manufacturers sites recommend a low OG starter to condition the yeast cell walls for optimum budding to build yeast cell count.