Over the years, I have measured the total acidity of each variety and experiment with balancing acidity. Tannins are balanced more by taste because they, for me, are more trouble to measure. So, sometimes I blend then ferment to save barrel space. Actually, though, as time goes by, I like to ferment individually and then blend. This means, I am gradually trying to plant what varieties blend best and favorably grow. Granted, my goal is not to pump and dump cider and be a millionaire, but more as a lifelong art. I love the trees and growing things. It is so much fun. This forum has been a valuable learning site.