Rhubarb Jam for 6 Half-Pint Jars

Instructions:

1. Wash the rhubarb thoroughly, trim the ends, and chop the stalks into uniform ¼-inch pieces.
2. In a wide-bottomed heavy pot, combine the chopped rhubarb, sugar, lemon juice, and lemon zest. Stir over medium heat until the sugar completely dissolves and the rhubarb softens.
3. Increase heat to medium-high and bring the mixture to a rolling boil, stirring frequently. If excessive foaming occurs, stir in the butter to reduce surface tension.
4. Continue boiling for 15–20 minutes or until the mixture reaches 220°F (104°C) on a digital candy thermometer and sheets off the spoon in a thick layer.
5. Ladle the hot jam into sterilized half-pint canning jars, leaving ¼ inch of headspace.
6. Run a bubble remover tool around the inside of each jar, wipe the rims clean, center the lids, and screw on the rings until fingertip-tight.
7. Process the jars in a boiling water bath for 10 minutes. Remove and let sit undisturbed for 24 hours.