"Expired" Imperial yeast and yeast calculators

[brownni5]

I overshot my gravity yesterday (by a lot) so I added water to bring it down and decided to keep a liter of wort for a starter. Time to get that A38 Juice going! Package date was 5/31/19 - so nearly 7 months old (it's been hanging out in my fridge since August). They now say Imperial is good for 4 months, but I disagree - it's a monster for longer than that! I deal with expired (cheap/harvested) yeast all the time, and haven't seen 7- month old yeast take off that quickly before. My yeast calculator said I had -87 billion cells (antimatter!), so that was clearly wrong.

Two take-aways: Imperial yeast is a great product and yeast calculators will only take you so far.

 

[IslandLizard]

Yeast being "good" is very qualitative, and subjective too.

Without doubt, viable yeast count starts to go down right after the yeast is done propagating. The rate it goes down varies wildly by packaging and storage methods. Traditionally a 10% decline per month is accepted, and typically used in yeast calculators. But many yeasts/storage methods have proven to fare (much) better. For example, WhiteLabs' Pure Pitch sleeves will only decline 3% per month for the first 3-6 months. After hanging out in the fridge for over 2 years I've revived such old WLP lager yeast to pitchable quantities in 3 steps.

Switch to a better yeast calculator, anti-yeast is hazardous to your beer.

Aside from Mr.Malty, this is the one I've been using:
BrewUnited's Yeast Calculator