I baked a cake for my son's third birthday with a buttercream frosting, which, as we all know, often comes out yellow thanks to the butter. I put several drops into my double batch of frosting, and it did noticeably whiten. I will say the my frosting wasn't a perfect white, but I didn't need it to be, and I wanted people to know I'd made it from scratch, so this at the very least brightened the frosting beautifully and did not affect taste or smell.