I suspect it's hardening around the skin of the potato (hence can't eat the skin) and essentially letting the potato steam itself?
Kind of like if you deep-fried it submerged in oil, but with even less ingress, and much less than boiling.
I commented this elsewhere and someone suggested sous vide ought to be very similar then, of course. (Added benefit perhaps: you can eat the skin!) Only difference might be that the rosin can get hotter, more like oil, than boiling water circa 100C.
I suspect it's hardening around the skin of the potato (hence can't eat the skin) and essentially letting the potato steam itself?
Kind of like if you deep-fried it submerged in oil, but with even less ingress, and much less than boiling.
I commented this elsewhere and someone suggested sous vide ought to be very similar then, of course. (Added benefit perhaps: you can eat the skin!) Only difference might be that the rosin can get hotter, more like oil, than boiling water circa 100C.