"It's Old Bean Paste" being a fancier way of saying it's own poo paste, though technically it's pretty much what it is, old or stale paste.
Basically in this thread we theorize and discuss, for the sake of any future story with this kind of element on it, what could happen if a yukkuri was feed only that.
The first thing to consider is that the yukkuri must NOT be aware that's what it's eating, or else we know that the only thing this will lead is to accumulate grief and stress, leading to anti yukkuritis, so taking advantage of the short term memory is key here to make a long term test.
The second thing is that it should be it's own, this isn't a "just give any yu shit" kind of experiment, the idea is to see if "something" happens if the old paste is reintroduced back into it's system, after all the usual consensus is that many times yukkuri shit out bad memories that can be expunged or at least the recent recalling of it (sometimes a lingering core memory remains on it's paste core so an event can't trigger back the memory regardless if the yukkuri discarded the original paste containing it long ago.)
Feeding yu poo from other yu's kinda negates the purpose of this research, though it could be done as a side research to see what effects that would have on the manjuu golem.
Overall that's pretty much it, theorize, discuss and such, for funzies and maybe inspire creativity.