Put all the ingredients in a saucepan set over low heat. Let the sugar dissolve, and then bring to the boil. Simmer for a few minutes, then remove from the heat and let the ginger infuse for several hours, or overnight for a stronger cordial. Strain, bottle, and refrigerate. This makes an excellent flavouring for ice creams and custards.
Do not throw the ginger away, either, but chop it