- 4 pounds rhubarb, trimmed, rinsed, and cut into small chunks
- 4 cups sugar
- 1 1/2 cups water
- 1 lemon, halved and juiced, seeds reserved in a cheesecloth pouch or tea ball
- 1. Sterilize the jars for canning by boiling them and their lids. Place a small plate in the freezer.
- 2. Place the fruit, sugar, water, and lemon juice, spent halves, and seeds (they provide the necessary pectin) in a large bowl and set aside at room temperature for 1 hour.
- 3. Pour the contents of the bowl into a large pot and bring to a boil over medium-high heat. Continue to cook, stirring the jam constantly, for about 15 minutes. Skim the foam from the surface as the jam cooks.
- 4. Drop the heat to medium. Hold the jam at a constant simmer, checking frequently to make sure the jam isn’t scorched at the bottom of the pot. After 15 minutes, check to see if your jam has set by placing a small spoonful of jam on the plate from the freezer. The rhubarb jam is set when it holds its shape on the cool plate. If it seems loose, continue cooking over medium-low heat until set.
- 5. Remove the seed bag and lemon halves and compost them. Place the rhubarb jam in sterilized jars, filling them to the bottom-most ring. Gently tap the bottom of each jar on the counter to release any air bubbles. Using a damp clean towel, wipe the rims of the jars and secure the lids and rings. Process in a water bath for 5 minutes if using pint jars, 10 minutes if using quart jars. Remove the containers with tongs and let cool on the counter. When the jam is cool, remove the metal rings, check for proper seals, and label with the date and contents. Store the rhubarb jam in a cool, dark cupboard until ready to use for up to 1 year.