I've done a wheat with cranberry extract, and a different wheat with canned raspberries. I thought the extract was good, but I appreciated the real thing a little more.
To 23L, I would add two 15 oz cans of Oregon whole fruit (raspberries, blackberries, peaches, etc). It would be noticeable but somewhat in the background. Three cans is in your face a little more (what I did). Next time it'll be 2 cans. The nice thing about canned is its already sanitized. You just give it a 3 second zip in a sanitized blender to break it up a little. Oregon sells 3 lb cans of puree too, its just a little more expensive.