Whoa! Here we go!! Don't tell me .. you're a student of Roger Boulton's at Davis, right?? This is a VERY interesting topic, as is co-pigmentation. But, I don't belive as much is "really" understood about co-fermentation. Other than that they have been doing it forever in the Rhone with "certain" varieties! But, what really makes it work? What variety has co-factors for who??? I've begun to wonder if, here in Oregon, maybe Pinot Gris (glut) might have some good co-factors for Pinot Noir (tricky to get deep color, sometimes). Wouldn't THAT be nice!! Barney .. let's get the Beaver Nation ON IT, ok?? :^)
Charlie