To make Pink Grape syrup, peel the zest from two large pink grapefruits.Squeeze the juice out of them and measure how much you get out. Pour this into a saucepan and add a lot of purple caster sugar. Squeeze the oils out of the zest down over the sugar and juice and throw in the peels too. Heat, stirring, until all the sugar has dissolved. Remove from heat and allow to cool before pouring your grape sugar mixture into a clean glass bottle