That may be because the juice is cold. I do often heat my juice a little so it's warm in cold weather or if it's made from refrigerated veg. I wouldn't boil it, but you could bring it to near boiling point for a short time. Try just heating it a little and see if that helps, or maybe use less greens if they are a problem, but since they are the most nutritious part, you need to get as much as you can. Maybe drinking less at a time would help too