Season would be about over here. I tapped black walnuts one year. Sap flowed like a maple. Slightly sweet also like maple. When I cooked it down it turned more of a dark yellow, sort of a dull yellow Lemon lollipop color. It did have a very buttery flavor. We only made a couple pints one year. I had talked to the folks up at Cornell about it and back then they acted like I was speaking alien. I cited him the book that mentioned it. "Edible Plants of eastern North America" The guy said he was going to read up on it and get back to me. That was about 2003.