Prepare a boiling water bath and two-pint jars. Place a small plate into your freezer ( this will be used to test the jam at the end of cooking to determine if it has reached set).

Combine rhubarb, sugar, orange juice and zest in a large, non-reactive pot.

Place over high heat and bring to a boil, stirring regularly. Once the mixture is bubbling rapidly, reduce temperature to medium-high and simmer for 15 to 20 minutes, until the mixture has thickened considerably.

When the contents of the pot have reduced by approximately 1/3 to 1/2, slide the pot off the heat. Remove your small plate from the freezer. Drop a small amount of the jam on the center of the plate and let it rest for 30 seconds. Tip the plate to one side; the jam should be a soft gel that moves slightly. If the mixture is thin and runs down the plate, the set is too soft.

Once the time is up, pull the plate out of the freezer. Gently nudge the mound of jam. If it holds its shape, the jam is done. If your finger slides right through it, it needs a bit more cooking time.

When you've determined that the jam has sufficiently thickened, remove the pot from the heat.

Pour the jam into hot jars. Leave 1/4-inch headspace. Wipe rims, apply lids and rings and process in a boiling water bath canner for ten minutes.

When time is up, remove jars from water bath and let them cool on a folded kitchen towel.

Sealed jars can be stored in a cool, dark place for up to one year.