Q: If a recipe does not explicitly say to use sifted flour, is it a good idea to sift anyway? I typically bake from American recipes so I'm measuring based on volume, not weight. I think sifting expands volume though I've never actually tested that.
A: Funny, I was just talking about this to my desk neighbor. Personally, I don't care for sifting, except in rare cases. However, what I always do is aerate the flour with a whisk to loosen it up. I am not 100% but I think sifting might be more important if you're a really infrequent baker and the flour really settles and compacts. Lastly, I want to implore every home baker to bite the bullet and buy a kitchen scale. I promise you it'll be the best $25 you'll spend - if for no other reason but having way fewer dishes to wash than if you were relying on volume measure. OK, sermon over.
— Olga Massov, The Washington Post