Cut the watermelon skin into pieces.
Scoop out all the pink flesh and cut away the green peel.
Prick each piece with a fork and cut into equal-sized cubes.
Weigh the peel and make a note of the weight.
Make a mixture of water and slaked lime, using 20 ml slaked lime for every 3,5 litres of water.
Cover the watermelon peel with the mixture and allow to soak for two days.
Drain and soak in fresh water for two hours. Drain again.
Make a syrup with 500 g sugar for every 500 g fruit and one litre of water for every 500 g sugar.
Heat the water and sugar in a large saucepan and simmer for five minutes.
Add 45 ml lemon juice for every 1 kg fruit.
Meanwhile, bring another saucepan of water to the boil and add the watermelon peel, a few pieces at a time, so that the water does not go off the boil.
Boil for 10 to 15 minutes until the peel is transparent and tender.
Transfer the pieces from the water to the boiling syrup.
It is very important to do this in batches so that the syrup does not go off the boil.
Once all the peel has been added, simmer with the lid on for one hour.
Remove from the heat and allow to stand for six hours.
Remove the lid and heat the mixture again.
Allow to simmer until the peel is light and the syrup is thick.
Spoon into sterilised jars, fill with syrup and seal.
Makes 2 to 4 jars.
Add pieces of ginger to the syrup when cooking for extra flavour.
Leftover syrup is delicious drizzled over baked sweet potato and over pumpkin.