I believe that's spent grain from brewing, solubles is soluble fiber. It's not a bad ingredient, it's in a lot of animal feed.
Lazy can correct me if I'm wrong.
Opinion: I feed Dumor 20% Grower crumble with Oyster shell on the side.
It's inexpensive at $20 / 50lbs. Every now and then, the bags in the store are too old, so I pick up Flock Raiser instead (for $5 more). I was surprised it looks / smells exactly the same, and the birds don't think there's...