tedburn, I do notice similar issue with taste. I have many citrus varieties grafted on my large lemon tree (30+) and the Shiranui/Sumo fruits do taste different on the lemon tree, not as sweet as the other Shiranui grafted on my other citrus trees (lime, sour orange, mandarin, grapefruit). Shiranui grafted on mandarin seems to have the sweeter taste than the fruits grafted on lemon tree. Ponkan on the same lemon tree seems to taste sweet and good.