GRAPE-PLUM JELLY

By Tessie2



3½ pounds ripe plums
3 pounds ripe concord grapes
1 cup water
½ teaspoon butter or margarine (optional to reduce foaming)
8½ cups sugar
1 box (1¾ ounces) powdered pectin

Wash and pit plums; do not peel. Thoroughly crush the plums and grapes, one layer at a time, in a saucepan with water. Bring to a boil, cover and simmer 10 minutes. Strain juice through a jelly bag or double layer of cheesecloth. Measure sugar and set aside. Combine 6½ cups of juice with butter and pectin in large saucepan. Bring to a hard boil over high heat, stirring constantly. Add the sugar and return to a full rolling boil. Boil hard for 1 minute, stirring constantly. Remove from heat, quickly skim off foam and fill hot, sterile jars, leaving ¼-inch headspace. Wipe jar rims. Adjust lids and process for 5 minutes in boiling water bath.
Yield: About 10 half-pint jars