Just bottled a batch of DB that is all blackberry. Went with 1 cup sugar per gallon, which is a little sweeter than I like, but friends love it that way. Also, this time I added 3 tbsp of glycerin (to 3 gallons) to improve body. Improved the mouthfeel, but added to the sweetness. Next time I think I'll use just 2.5 cups sugar per 3 gallons. Compared this to the "Quad Berry" version and the blackberry is noticeably deeper in color.