FWIW, I saw a similar post on reddit with a pic, white stuff at the edge of the nylon bag being used for filtration (inside and outside of the bag). The consensus was that thc-a can occasionally be separated out in a single pass, rather than pressing into rosin, then pressing the rosin.
Thanks, thats useful. It was a long slow press and low temps in an over stuffed bag, so...
Anyway, pre press and more appropriate bags have been ordered!
NV pre press, obviously, because I am a fanboy (and its the one thats made to go with the plates I have)