Chop the cleaned rhubarb and place in a large, tall saucepan with the gelling sugar, lemon juice, lemon zest and water.
Bring to a boil over medium heat, stirring constantly. Let it simmer (while continuing to stir) for 4 to 5 minutes. The mixture may foam, so make sure your pan is high enough.
Turn off the heat and allow the mixture to settle. Scoop the jam into the jars with a ladle and immediately place the lids on the jars, then turn the jars upside down. This will push the air out of the jar and help it keep longer.
Leave the jars upside down for about 5 minutes before moving them. Allow the rhubarb jam to cool thoroughly.
Tips
If you have no gelling sugar in the house and prefer not to use powdered or liquid pectin >> instead, add the juice of an extra lemon and let the jam simmer for half an hour longer.
Is your rhubarb jam pinker than mine? That may well be true. Rhubarb can vary quite a bit in color, from green-yellow to red-pink. Green rhubarb is more acidic than red rhubarb.
How to store
Unopened jars can be stored in a dry, dark, cool place for up to one year. Opened jars should be stored in the refrigerator and consumed within 3 weeks.