Directions
Preparation:20min  ›  Cook:2hours20min  ›  Extra time:1day20min  ›  Ready in:1day3hours 

1. Using a sharp knife, cut a thin slice from each end of each fruit and set aside. Cut the grapefruit into eight wedges, each orange into six and the lemons and lime into four wedges each. Cutting across each segment, thinly slice all the fruit, removing and reserving any pips.
2. Put the end slices and pips into a square of muslin, tie securely to form a bag and place in a large bowl with the sliced fruit. Cover with the water and leave to soak for 24 hours.
3. Next day, transfer the contents of the bowl to a stainless-steel or enamel preserving pan and bring to the boil. Reduce the heat and simmer for 2 hours, or until the peel is very soft—test by pressing a piece, after cooling, between your thumb and forefinger.
4. Remove and discard the muslin bag and add the sugar to the pan. Stir over medium heat until the sugar has dissolved, then bring to a full rolling boil and continue boiling for about 20 minutes. Remove the pan from the heat and test if setting point has been reached: 105°C on a sugar thermometer (see Cook's tip).
5. Remove the saucepan from the heat and skim off any scum from the surface with a draining spoon. Leave to cool for about 5 minutes, or until a thin skin starts to form on top of the marmalade. Stir gently to distribute the peel evenly.
6. Ladle into warm sterilised jars, then cover and seal. When cold, label the jars and then store in a cool dark place. Use within 1 year of making. Once opened, store in the fridge and use within 1 month.

Cook's tip

If you haven't got a sugar thermometer, spoon a little of the marmalade onto a chilled saucer, cool for a few seconds then push a finger across it. If the surface wrinkles, it has reached setting point. If not, boil the marmalade for a further 5 minutes, then test again.