The next day, transfer the marmalade mixture to a large saucepan and on a medium heat simmer gently until the orange peel is soft and the water content is reduced by about half. You can test if the peel is right by tasting it. The orange peel will also look slightly see-through and will sort of go more opaque.
When the peel is soft, check that you have about 500ml of water/liquid left. If not, simply top up the water with more water or the orange juice you collected yesterday.
Take out the muslin bag with orange pips and discard.
The next step is to add the sugar and let it dissolve properly. Check on the back of a soup spoon that all the sugar crystals have dissolved before you move to the next step.
Once the sugar has dissolved, bring the marmalade to boil and boil for about 10-15 minutes or until you reach the setting point.
Check your setting point using a cold plate and a spoonful of the marmalade.
Once you are satisfied that your marmalade will reach the setting point, take it from the heat and leave it to stand for about 10 minutes. This will help to distribute the orange peel more evenly once potted.
Divide between 4-5 jam jars, seal and let to cool down properly before storing away in a dark, cold place. Use within 12 months (or two years maximum).