Its time for the next update on my drying kveik experiment. As a quick bit of background, 3 months ago I dried some Voss Kveik using a home food dehydrator. I have been monitoring the viability of the yeast on a monthly basis since then:
Viability continues to decrease at 6-8% per month, with viability currently at 76-78%. This is consistent with the past two months, with yeast viability decreasing to 50% viability after 6 months. 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.
As per my estimate last month, this data is consistent with a maximum usable lifetime (e.g. ~1% viability) of ~40 months. That is over 3 years.