Combine the first two ingredients in a nonreactive medium saucepan and cook until rhubarb is tender, about 8 to 10 minutes. Drain.
Combine cooked rhubarb with remaining ingredients in a large, 12-inch nonreactive skillet and bring to a boil. Reduce heat until mixture bubbles steadily and cook until the temperature reaches 218 to 220° F on an instant-read thermometer. Stir frequently.
Remove from heat and skim off any foam. Let sit for 5 minutes and then ladle into sterilized jars. Cool and then freeze or the jam can be water-bath canned per the instructions, no less than 10 minutes, with the canning jars.
Servings: 6 cups