Once you get no more vapour out of the pipe, wait 10-15 minutes so you know you're seeing straight. Then, turn your torch up and heat the residue directly and observe. If it quickly turns brown/black (burns), it's organic material (likely fat or stray plant matter).
If it doesn't change noticeably under direct heating after 10 seconds, it's likely NaCl (or some other ionic sodium compound developed from back salting). To test this, throw a little bit of water through your device.
If the chalky substance dissolves or appreciably disperses in water, it's salt/lye. If not, then it's probably some other insoluble sodium compound.
Anyway, it can probably be avoided by dialling back the NaOH in the mini a/b (try 10-15g rather than 50). Additionally, after precipitation, you could wash the crystals with a mild sodium carbonate solution at room temp.
"Laws alone can not secure freedom of expression; in order that every man present his views without penalty there must be a spirit of tolerance in the entire population." -Albert Einstein
I'm not a big fan of SWIM. I mean, I've never met the guy, but any time I hear about him, he's doing something sketchy.