In a large pot, place the rhubarb and sugar. Add the citrus pulp and peel. Bring to a boil over medium high temperature, stirring to prevent scorching. Immediately lower the temperature and cook, uncovered, at a slow gentle boil until mixture thickens and reaches a sustained temperature of 217°F on a candy thermometer (see Note below for alternative testing method). Stir mixture regularly to prevent scorching. Be patient, this can take an hour or so. The marmalade may be cooked to a temperature of 220°F but it will be a thicker marmalade and less pliable to spread than if it is cooked to 217°F.
Meanwhile, fill the hot water canner about one-third to one-half full of water. Cover and bring to a boil to have it ready for the filled jars.
Yield: Apx. 7 half-pint bottles
NOTE 1: If you don’t have a candy thermometer, place 2-3 freezer-safe saucers in freezer. To test for doneness of the marmalade, place a small amount of marmalade on chilled saucer and swirl saucer around. Let marmalade sit, untouched, for about a minute, then gently push your finger through the marmalade. If the marmalade holds its shape (i.e., does not immediately run back together after the finger has been removed from the marmalade), it is set and ready to bottle. If not, continue to cook mixture, repeating the “chill” test about every 3 minutes or so (always removing the pot from the heat while conducting the chill test) until the marmalade passes the “chill” test. Do not overcook as it will result in a very thick marmalade, dark in color.
Note 2: After jars have completely cooled, if there are any on which the lids have not curved downward, refrigerate them and use within one month.