Hi cheezz...
I have a recipe for Rhubarb-Orange Jam. I think you just juice the grapefruit or remove the membrane from the grapefruit and use the juice and the pulp. Do you remember if there was any pulp in the jam you had? I think you could probably go either way and it would be okay.
I haven't made the recipe below, it is from my new book. smileys/smile.gif
Rhubarb-Orange Jam
2 oranges
5 cups finely chopped rhubarb
1 package (1.75 oz) regular powdered fruit pectin
6 cups sugar
Using a vegetable peeler, remove peel from half of one ornage. Cut peel intovery thin slivers, about 1 inch long, and set aside. squeeze joice from both oranges into a measure, adding water if necessary, to yield one cup.
In a large, deep stainless steel pot, combine orange juice, slivered orange peel and ghubarb. Whick in pectin until dissolved. Bring to a boil over high heat, stirring frequently. Add sugar all at once and return to a full rolling boil, stirringconstantly. Boil hard, stirring constantly, for 1 minute. Remove from heat and skim off foam.
Ladle in jars and process them for 10 minutes.
Makes about seven 8-ounce jars