Yeast Viability Percentages on Jamil's Calculator

[Stevorino]

I bought a pack of Wyeast Saison yeast at the LHBS today and didn't check it's 'Born on Date' until I got home -- which ended up being March 5, 2009. Usually my LHBS has fresh yeast supplies, but I guess Saison isn't very popular.

Jamil's Calculator is telling me that the viability is only 33% - which seems quite low.

When I hit the smack pack thing, it blew up pretty quickly -- 2 hours later, if I shook the pack at all, the package would blow up and look like it was about to pop -- seems pretty viable to me.

I went ahead and pitched it into my 2.1 liters of 1.040 Starter w/ Yeast Nutrient on a Stir Plate. It should be on the stir plate around 40 hours before pitching to the real deal on Friday afternoon.

According to Jamil's Calculator, if the Viability is 65% or more, I'm golden, anything less and I'm technically underpitching -- Am I screwed?

[Quin]

If I read this correctly, are you saying that your starter is half the size it should be (33% vs 65%). You probably should step it up after 24 hours if that is the case.

[Stevorino]

If I read this correctly, are you saying that your starter is half the size it should be (33% vs 65%). You probably should step it up after 24 hours if that is the case.

Technically, the Calculator is telling me that the viability is so low (33%) that I couldn't build a proper starter with just one pack of yeast - It was pushing 3 packs at that viability.

I don't think the viability was that low though -- 12 hours after pitching into my stirplate starter, this thing is going absolutely nuts -- maybe the best starter I've ever had.

I'd go get another vile or step it up again, but after listening to the Jamil show, I think I'd rather underpitch a tad then overpitch because the esters in this style are so crucial.

[RJH311]

sounds like you got lucky because I dont think a 33% viability smack pack would puff up that quick. I think you'll be fine with the 2 liter starter. Shit we all used to pitch straight from the pack with no problems.

[MattSF]

yeah i've always thought the viability numbers on the Calculator to be rather aggressive. It seems that if you didn't get your yeast right from your local microbiologist an hour ago, you might as well take up a new hobby. i keeeeed!

Also, the White Labs vials don't have a date of production, they have a "best before" date. Is that date 6 months from the production date? 3 months? anyone know?

[Stevorino]

yeah i've always thought the viability numbers on the Calculator to be rather aggressive. It seems that if you didn't get your yeast right from your local microbiologist an hour ago, you might as well take up a new hobby. i keeeeed!

Also, the White Labs vials don't have a date of production, they have a "best before" date. Is that date 6 months from the production date? 3 months? anyone know?

I believe 6 months

[Chupa LaHomebrew]

I agree that the reduction in viability due to age seems to ba a little on the pessimistic side, as far as my own experiences go. If a yeast is old enough to get down to 10-20% then I usually add a 1 quart starter step to get it back up to 1 tube's worth, and then do another step if necessary.

[Stevorino]

I agree that the reduction in viability due to age seems to ba a little on the pessimistic side, as far as my own experiences go. If a yeast is old enough to get down to 10-20% then I usually add a 1 quart starter step to get it back up to 1 tube's worth, and then do another step if necessary.

That's a good idea - definitely what I should have done. I think for this batch though, I'm going to let it go and hope it makes it. It should be fine given that I'm fermenting in the 70's/80's.