Scott,
The flavor of these blackberries are excellent. Kansas soil at times gives greens a metallic flavor when you first till a garden but after the first year or two it’s gone. I suspect those blackberries of yours are doing something similar at your house. The dirt may have excess nutrients that plant picks up. An example of one such mineral is cobalt which hybrid corn cannot pick up I’m told. Open pollinated corn can pick up cobalt and is used to prevent brucellosis according to many experts. I had problems with my honeoye strawberries giving that diet kool aid aftertaste and eventually stopped growing them.