Fraction of a harvested slurry's cells still alive on a given day.
Uses the same curve as packViability with the liquid constant,
counting from the day the yeast came out of the fermenter, since a jar of
slurry has no pack date. Sharing the decay model means a repitched
culture's viability can't come out differently depending on who asks.
Why the liquid constant
The two figures in VIABILITY_RETENTION_PER_30_DAYS describe two packaging
states, not two organisms. Dry yeast's 0.96 per 30 days is for a
vacuum-packed cake at roughly 5 % moisture, made for shelf life, with cells
that are metabolically dormant and using almost nothing. Harvested slurry is
the opposite: fully hydrated, suspended in beer, still respiring at fridge
temperature, and using up its glycogen and trehalose as it sits. That's the
same situation as a liquid pack, so it gets the liquid figure, 0.79 per 30
days.
There's no source for this
There's no published decay constant for homebrew-harvested slurry, and it
wouldn't be a single number if there were. It depends on how much beer and
trub came with it, whether it was rinsed, how cold it was kept, and how hard
the ferment it was cropped from worked the cells. Slurry taken at high
krausen off a healthy 1.048 ale is in better condition than the same strain
scraped off the cake after four weeks under a lager.
So the liquid curve is a reasoned default, not a measurement, and it's no
better than the ±15 % the module header gives for everything downstream of
starterGrowth. Callers should show it as a whole percentage, as a
rough indication of freshness.
Fraction of a harvested slurry's cells still alive on a given day.
Uses the same curve as packViability with the liquid constant, counting from the day the yeast came out of the fermenter, since a jar of slurry has no pack date. Sharing the decay model means a repitched culture's viability can't come out differently depending on who asks.
Why the liquid constant
The two figures in
VIABILITY_RETENTION_PER_30_DAYSdescribe two packaging states, not two organisms. Dry yeast's 0.96 per 30 days is for a vacuum-packed cake at roughly 5 % moisture, made for shelf life, with cells that are metabolically dormant and using almost nothing. Harvested slurry is the opposite: fully hydrated, suspended in beer, still respiring at fridge temperature, and using up its glycogen and trehalose as it sits. That's the same situation as a liquid pack, so it gets the liquid figure, 0.79 per 30 days.There's no source for this
There's no published decay constant for homebrew-harvested slurry, and it wouldn't be a single number if there were. It depends on how much beer and trub came with it, whether it was rinsed, how cold it was kept, and how hard the ferment it was cropped from worked the cells. Slurry taken at high krausen off a healthy 1.048 ale is in better condition than the same strain scraped off the cake after four weeks under a lager.
So the liquid curve is a reasoned default, not a measurement, and it's no better than the ±15 % the module header gives for everything downstream of starterGrowth. Callers should show it as a whole percentage, as a rough indication of freshness.