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.
Pectin is found in pith, pulp and pips of citrus fruits (bitter oranges have plenty), so it’s very important that the trimmed pith should be chopped for better extraction and tied in a loose muslin bag (so water circulates) together with pips and added to the pan. Simmering extracts pectin. After simmering, squeeze bag between two dinner plates over the pan to extract all the juice.
Fast boiling is the secret of a good flavour and set. Test marmalade after 15 minutes and then every 5 minutes after that. Draw the pan off the heat before you test it will do no harm at all.
Don’t pot marmalade straight away unless you marmalade to cool for about 20 minutes when a skin will form on the surface. Stir once and the peel will hang suspended in the jelly, then pour into jars.
Cover marmalade with waxed discs and a clean cloth when hot. Seal with Cellophane covers when cold to reduce risk of condensation which encourages mould.
Use the whole fruit method to make a chunky marmalade. Oranges can be boiled whole and chopped after cooking. This is also the method to use with frozen oranges€”no need to thaw.
For an improved flavour in any orange marmalade recipe, coarsely crush 1 tablespoon coriander seeds, tie in a muslin bag and suspend in the pot with the simmering oranges or peel. The flavour is deliciously aromatic. Discard the muslin hag before adding the sugar to the recipe.