I experienced this very same thing three years ago when I first bought my farm. I got a bag of the generic gamefish food from Tractor Supply and the BG would do just what yours did - grab it and spit it right back out.
I ended up buying a more expensive feed - a 50 pound bad of Burris feed, and they hammered it the very first time. Ewest is right on - get a quality food and the fish will love it, plus it'll be much better for them.