- 1 quart strawberries
- 1 quart red raspberries
- 1 pint blackberries
- 7 cups sugar
- 1/2 tsp butter or margarine, if desired (added to reduce foaming)
- one 3-ounce pouch certo liquid fruit pectin
Discard stems and crush enough strawberries to measure 2 cups of crushed berries. Crush enough raspberries to measure 1 cup. Crush enough blackberries to measure 1 cup.
Add the prepared fruit to a 6- or 8-quart saucepan. Stir in the sugar and butter or margarine. Stirring constantly, bring the mixture to a full rolling boil (a boil that doesn't stop bubbling when stirred) on high heat.
Stir in pectin quickly. Return the mixture to a full rolling boil and boil exactly 1 minute, stirring constantly. Remove from heat. Skim off any foam with a metal spoon.
Ladle the jam into one jar at a time, leaving 1/4-inch headspace. Wipe jar rim with a clean, damp cloth. Attach lid. Fill and close remaining jars. Process in a boiling water canner for 10 minutes (15 minutes at 1,000 to 6,000 feet; 20 minutes above 6,000 feet).