2kg oranges and grapefruit (3 large grapefruit, the rest oranges)
2kg granulated sugar with pectin (i.e. Silver Spoon® jam sugar)
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Method Prep:30min › Cook:4hr › Ready in:4hr30min
Use a grater to remove the peel from all the oranges and put the peel to one side for now.
Quarter the oranges, grapefruits and lemons, remove all the pips, and then squeeze all the juice from the juice into a jug. There should be about 1 litre of fruit juice from this amount of fruit.
Put all the remaining fruit pulp and carcasses into a large (5 litre plus) pan and add the 4 litres of water to cover the fruit. Do not add the sugar yet!
Leave the pan uncovered and heat up to boiling point; then add the jug of fruit juice (minus any floating pips) to the pan along with the grated peel from earlier. Bring the mix back up to the boil and then simmer uncovered for about 2 hours or until the contents are reduced by half. Check to make sure the peel is really tender.
When the mix is ready, remove from the heat and carefully remove all the fruit carcasses with pulp and put it into a colander on top of a large bowl. Squeeze all the carcasses and pulp in the colander with the back of a large spoon to extract all the juice into the bowl. Discard the fruit skin carcasses and any remaining pips and then put the rest of the pulp and the extracted juice back into the pan again.
Before putting the mix back on the heat, and while the mixture is still warm, add all the jam sugar, stirring continuously to make sure it’s evenly mixed and completely dissolved.
Return the pan to medium then high heat and continue stirring constantly while the mix is heating up slowly to boiling point, this will ensure the sugar does not burn on the bottom of the pan during heating. Once the mix is boiling vigorously with a thick layer of froth on top that cannot be stirred away (over 105 degrees C), this will start the setting process using the pectin content in the mix. Continue to boil the mix vigorously stirring all the time for 15 minutes and then switch the heat down to simmer it for another 90 minutes or until there’s about 2 to 2.5 litres of mix left. The mix should now look relatively clear.
Test for the setting point by dropping a little marmalade on a cold plate or the back of a cold spoon from the fridge, if you push it with your finger and it wrinkles, it is ready. If not, then boil for a bit longer.
Transfer the mix to sterilised jars while it's still hot and seal the lids immediately. Leave to completely cool overnight in a cool dark place.