I am now four months into my drying kveik experiment. Four months ago I dried some Voss Kveik, and have been providing monthly updates on its viability since. For those wanting the back-story:
Drying Kveik – Viability at 4 Months
Viability continues to decrease in lock-step with past months, at a rate of 6-8% of viability lost per month. Based on this, I
At this rate we should reach 50% viability somewhere between 6 and 7 months post-drying. I would estimate that would be enough to pitch this yeast directly, without a starter. For longer storage, a starter is likely 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.
A Brief Note on Viability Testing
I should also mention that my viability numbers are worst-case scenarios based on the trypan blue method I am using. Trypan blue will lightly stain some viable cells, as well as cells undergoing cell division. This is apparent in the image to the left, where the mother cell is stained with trypan while the daughter cell is not. This staining is unlikely to be due to death of the mother, as the mother and daughter cells still share a cytoplasmic connection – e.g. if one dies, so does the other.
This is a well known limitation of trypan blue staining, but I am scoring all cells with above-average staining as dead. As such, the true viability is likely slightly better than I am measuring – perhaps by as much as 5%.