Bring 500ml water and 500g castor sugar to boil in a saucepan. Simmer gently for 10 minutes or until all the sugar crystals are dissolved. Allow to cool and then store in a sterilised jar in the refrigerator. It keeps almost indefinitely. Sugar syrup is used when making sorbets and poaching fruit. It is often infused with cinnamon and such, depending on the recipe. If the proportion of water to sugar is equal you can make more or less, as required.