Question: Sifting Flour For Cake
By: Diana
Published: March 14, 2010

do you sift flour and then measure or measure then sift/

Answers:
Sonia R. Martinez

Usually you meassure first and then sift.  Some recipes call for sifting and others don't... I think it is a throwback from the days when flour was much denser than today's flour.  I've successfully baked cakes that called for sifting flour without sifting and didn't notice much of a difference.  If I use cake four then I never sift.
Chef Maven Leah...

Depending upon which types of flours you use and which recipes you are using, there can be a great different in the amount of flours measured out if you don't sift vs. sifting.
Feel free to read my article about flour here: http://thechefmaven.com/2008/04/05/differences-in-flour-explained-sift-out-your-flour-issues/
You need to measure, sift - measure once again, then add salt, baking powder, etc. then sift again. This process will give you light and airy cakes.
In my own tests, I have measured - and sifted - and actually found a 1/2 cup of flour difference (of extra flour) once I sifted - now imagine that in an angel cake recipe for example! - You would end up with a denser angel cake than you meant to make.
For those flours which have been sifted - I would sift once with the added salt and other dry ingredients.
Good luck with your baking!
Linda Owens

Measure first then sift the dry ingredients.  This gets rid of any lumps that could be in the dry ingredients before mixing.