I've been thinking about the kveik yeast strains, and how the rural Norwegian brewers selected yeast strains that could survive their brewing practices:
-brewing for special occasions, so long duration between brew days
-high gravity wort, high pitching temperature with minimal chilling capacity
-yeast must survive being dried and revived, with minimal sanitation
-no pure-culture technology to isolate individual strains from less desirable ones
So how did other historical brewing cultures influence the evolution of their brewing yeast?
We're told that in 1553, Duke Albrecht V declared that brewing was only allowed between St. Michael's Day (Sept. 29) and St. George's Day (April 23).
This had the effect of selecting for "lager strains" that can ferment at lower temperatures.
But what about the 5 months brewing pause? How did brewers maintain viable yeast without repitching into the next batch of wort?
They didn't mix the slurry with glycerol and store in a -80C freezer all summer
They didn't streak agar plates with a single yeast colony under a microscope
Did they dry some of the yeast and rehydrate it in the fall? Was is simply resident in the wooden barrels and sprung back to life with fresh wort?
Or simply revive some of the yeast slurry from underneath the stored beer?
The modern conventional wisdom is that yeast slurry should be repitched within 2 weeks, or else it will mutate and/or autolyse (cell death)
Is it possible that the fragile yeast strains that we have been re-purchasing every batch are much more hardy than we think? And that jars of yeast slurry in the fridge are perfectly good after 5 months or more?