I've got a persistent friend wish some good chemistry back ground whomkeeps arguing that STB methods or any method using spice yields spice contaminated with lye. I argue this is not so.
Any thoughts?

Sounds like fear mongering/misinformation. Lye is completely insoluble in non-polar solvents. In any case in case maybe you shook it or mixed and didnt let it stand enough for both layers to separate properly or pulled an emulsion layer together, it is possible small suspended droplets of the mimosa+lye solution come across. But thats super easy to clean, a simple sodium carbonate wash would make sure 100% that there is no lye. Check the FAQ out

Yeah, with a carbonate wash, there's really not going to be any lye... even without a carbonate wash, while there might be a tiny amount of lye (from water getting stuck in the naphtha as a sort of micro-suspension), it's still not going to be significant in most cases.

Swim uses a freezer temp ammonia wash (which works just fine for swim) but the principles the same. This friend says that the lye would still be in there. I feel that's not the case. And your fairly well validatig that. These were allmof arguments as well.

You dont even need to "feel" it, its a fact, any suspended lye would immediatey move to the acqueous layer when washing, whether its ammonia or sodium carb. Your friend is just wrong and theres no way around it