Mash berries, using a potato masher, until fairly smooth.

Measure out 5 cups berries.

Pour into a medium-size heavy saucepan.

Stir in pectin and bring to a full rolling boil, stirring constantly.

Add sugar and return to boil, stirring constantly.

Boil hard for 1 minute.

Ladle into clean jars and process for 10 minutes in boiling-water bath.