Put all the ingredients in a large pan and stir thoroughly to mix. Cover and set aside for at least a couple of hours for the rhubarb to ‘macerate’ – start releasing its delicious juices. You can leave the fruit for longer if you want, overnight would be fine.
Put 4 saucers or small plates in the freezer to chill, ready for testing the ‘set’ of the jam as it cooks. To sterilise the jam jars, preheat the oven to 120°C, fan 100°C, gas ½. Wash the jars and lids really thoroughly in hot soapy water, rinse well and arrange the jars upside down on a baking tray, tucking the lids alongside. Dry in the oven for 30 minutes. Remove from the oven and turn the jars the right way up (use oven gloves) without touching the rims, so they stay sterile.
Meanwhile, set the pan with the rhubarb over a medium heat, stirring as it comes up to the boil. Once the sugar has completely dissolved, turn the heat up to high and boil rapidly for about 10-15 minutes. Begin to test for setting after about 8 minutes. To do this, take a cold plate from the freezer and spoon on a little jam, tipping so it spreads to a thin layer. Allow to cool for 30 seconds. If the jam is ready, it will wrinkle up when you push it with your finger. If not, continue boiling for another minute or so before checking again. Keep stirring the jam, as it can catch on the bottom.
Once the jam has reached setting point, remove the pan from the heat and allow to cool and settle for 10 minutes. Stir well to distribute the bits of ginger then ladle the jam into a jug and pour into the warm jars, using a jam funnel if you have one. Seal tightly with the lids. Leave to cool completely before adding labels. Unopened jars keep for at least six months. Once opened, store in the fridge and use within a month.
1kg jam sugar
1 rounded teaspoon pectin powder/liquid
800g rhubarb, washed and chopped into 3cm lengths
Zest and juice of 2 medium blood oranges
150g stem ginger in syrup (drained weight)