Fatty residue on bottle nipple?

clrgrdfrk

I have been EP and bottle feeding since week 2 with DD and today with two of her bottles there has been residue on the nipple when I stop and burp her. There's nothing in her mouth, that I can see. I wipe it off and she finishes the bottle fine. It seems almost like fatty layer of BM when it's chilled before I warm up it, but I warm it up prior to giving it to her.

Any ideas?

Gilene2011

I think it's just fat from the milk. Or at least that's what I always thought.