The principle of marmalade making is the same as for jam, the fruit peel must be simmered until quite tender before the sugar is added. When ready a piece of cooked peel squeezed between the fingers will feel quite soft. This initial cooking is very important for sugar has a hardening effect and once it is added the peel ceases to tenderize any more.
Any white sugar, other than icing sugar, is suitable. Granulated sugar or the special preserving sugar give the best results and produce less scum. A proportion of brown sugar can be used, but not more than a quarter of the total amount. Once the sugar is added, stir until every grain is dissolved before boiling for a set. Any sugar grains remaining will cause the marmalade to go sugary on storage.