1 grapefruit 

1 Lemon

Tangold Mandarins 

2.5 litres water

7g tartaric acid

1.4kg granulated, cane sugar 

1. Weigh the grapefruit and lemon, then add the mandarins to make the weight up to 1.25kg. Scrub the fruit. Quarter and peel the mandarins. Finely shred the peel and divide it between two pieces of muslin 30cm x 30cm. Tie up the bags.
2. Peel the grapefruit and lemon.  Finely chop the grapefruit and lemon pith and peel. Add to the pan. Chop up the mandarin, grapefruit and lemon fruit Add to the pan with the acid.
3. Add the muslin bags to the pan.
4. Bring the pan to the boil with the lid on, turn down the heat and simmer very gently for 2 hours. 
5. Transfer the muslin bags to a sieve suspended over a bowl and leave to cool. Mash the cooked mixture in the pan and pour  this mixture into a jelly bag, suspended over a large glass bowl, letting it drip for at least 60 minutes, or until all the juice has been extracted. Add any juice from the rested peel. You should have between 1.4 and 1.7 litres of juice. 
6. Weigh a clean preserving pan and record the weight. Weigh the pan and look for a weight of the empty pan plus 1.4kg. Reduce the weight if necessary by gently simmering, checking the weight every 5 minutes.
7. Warm the sugar in an oven, 120C for twenty minutes.
8. Add the sugar to the pan of juice, dissolve the sugar, add the shredded peel and boil to a set, using the flake or thermometer  test, 10-15 minutes, Once setting point is reached, remove the pan from the heat and leave it to stand for 10 minutes and remove any scum. Gently stir the marmalade and pour into clean warm jars, up to the brim. Seal with new twist top lids. Leave the jars upright and undisturbed to set.