Two months ago I began an experiment in drying Kveik yeast for future use. At the 1 month time-point the dried kveik showed excellent viability. We’re now two months into the experiment, so its time for another viability test.
This test is straight-forward, I dried out some kveik slurry from a black IPA I made a few months ago using a cheap home dehydrator. The dried slurry is then stored in a home freezer, in a ziplock bag. Each month I take a small amount out, rehydrate it for 10 minutes in water, and then use a trypan blue stain to assess viability.
Drying Kveik – Viability at 2 Months
Viability continues to decrease at a slow rate. Viability is now at 84-88%, which is on-par with the ~8% drop in viability I observed last month.
Also consistent with last month, the yeast should decrease to 50% viability after 6 months of storage. I would guess that a 50% viability would be enough to pitch this yeast directly, without a starter. For storage longer than 6 months a starter is needed.
I don’t have enough data to calculate a maximum usable lifetime (e.g. ~1% viability). But I can make a rough estimate, based on the assumption of a 6 month half-life. If this is correct, the usable lifetime is about 39 months (3 years and 3 months)!