I have not been able to find the source of where I read/heard this, but can old yeast be boiled (or added to the wort boil) and used as a yeast nutrient?
Something to do with those old packs of munton’s that came with the beer kit. ;D
If so, would same hold true for a yeast slurry from a prior batch?
Maybe…as I understand it, the nutrient value comes from zinc stored in the yeast. There will only be a lot of zinc in there if the previous fermentation was healthy and built up a reserve.
IIRC, The Professor says he always adds some of the previous slurry to the boil on a new batch for that very reason.
But I don’t think he or anyone I’m aware of has actually done a comparison to see what is actually happening.