Tip the sugar, vanilla pod and seeds, wine and lemon zest into a wide pan and pour over 800ml cold water. Give everything a good stir to dissolve the sugar slightly, then set over a medium heat and gradually bring to boil, stirring occasionally. Turn up the heat to high so the syrup is boiling really fast, then turn off the heat and immediately stir in the rhubarb. Cover the pan with a plate or lid and leave to cool completely, then pour off 350ml of the syrup and reserve. Chill the remaining rhubarb and syrup.