To make these or any jars glisten, add 1 cup of vinegar to a deep pot of boiling water and dip each jar in the solution for 10 seconds. Then wipe clean with a lint-free towel.
Combine all ingredients in a large pot over low heat, stirring until the sugar dissolves. Simmer until the jam is thick and clear, about 1 to 11⁄2 hours. Toward the end of the cooking time, stir often to prevent scorching. Remove cinnamon; pour jam into sterilized jars and seal. Process 10 minutes in boiling water.