Makes 5 or 6 half-pint jars.
2 cups crushed strawberries or blackberries (about 1 quart berries)
4 cups sugar
1 package powdered pectin
1 cup water
To prepare fruit. Sort and wash fully ripe berries. Drain. Remove caps and stems; crush berries.
To make jam. Place prepared berries in a large mixing bowl. Add sugar, mix well, and let stand for 20 minutes, stirring occasionally. Dissolve pectin in water and boil for 1 minute. Add pectin solution to berry-and-sugar mixture; stir for 2 minutes. Pour jam into freezer containers or canning jars, leaving 1/2 inch space at the top. Cover containers and let stand at room temperature for 24 hours or until jam has set.
To store. Store uncooked jams in refrigerator or freezer. They can be held up to 3 weeks in a refrigerator or up to a year in a freezer. If kept at room temperature they will mold or ferment in a short time. Once a container is opened, jam should be stored in the refrigerator and used within a few days.
Note: If jam is too firm, stir to soften. If it tends to separate, stir to blend. If it is too soft, bring it to a boil. It will thicken on cooling.
From USDA #56