TO PREPARE JUICE: Sort and wash fully ripe mayhaw. Crush fruit, add water, cover, and bring to a boil on high heat. Reduce heat and simmer for 10 minutes. Extract juice.
TO MAKE JELLY: Measure juice into a kettle. Bring to a boil, add pectin and stir well. Bring back to a full rolling boil that cannot be stirred down. Add sugar, continue stirring, and heat again to a full rolling boil. Boil hard for 1 minute.
Remove from heat; skim off foam quickly. Pour jelly immediately into hot sterile canning jars to 1/4 inch from top. Seal and process 5 minutes in a boiling water bath. Makes 6 (1/2 pint) jars.