this is a question I had a week ago, which @glyph helped answer for me, which I will write here as I understand it for any future mushroom growers who have the same question as me
at first, my plan was to just do grain-to-grain transfers indefinitely, until I saw senescence start to happen. I thought once I saw senescence, like a batch that wouldn’t fruit, I would just get some new spawn from a supplier and restart the process.
@glyph helped me realize this is probably not a good approach, because senescence can come on slowly. Its like the mycelium getting old, and just getting less vigorous – so it could lead to less fruiting, easier contaminations, slower growth – and I wouldn’t necessarily be able to know when it was “starting”. In my initial plan of just doing grain to grain transfers indefinitely, senescence might appear just as the slow chtulian shadow creep of things slowly working progressively less well.
In practice, I was actually able to do grain to grain transfers for many months, and we are still seeing fruits. In fact some of the mushrooms fruiting in our chamber now came from an oyster mushroom I cloned last spring, and expanded via grain to grain transfers tens of times since then. so I’m curious what the practical limits are of after how many generations of g2g transfers you could expect to see senescence with oyster mushrooms,
but in practice, to avoid unknowable shadow creep,
I’m going to go back to the standard of having master cultures in agar and in liquid,
and a limited known number of generations each time from master culture to bulk inoculation.
Since I had good results with many g2g transfers, I might still experiment with doing a couple generations of g2g transfers, but I won’t do it indefinitely.
to close this post, here is a relevant thought experiment from the shroomery forum which makes me laugh,
source: Can Grain-to-Grain Transfers Be Done Indefinetly? - Mushroom Cultivation - Shroomery Message Board