2–3 quarts of blackberries, rinsed, hulled and crushed to make 6 cups
1 package powdered pectin
8 1/2 cups sugar
In hot soapy water, wash enough canning jars to hold 10 cups of jam, a pair of tongs and a ladle. Sterilize them just before you make the jam, either in your dishwasher if it has a sterilize cycle, or in a large pot of boiling water for 10 minutes. Drain them, mouth-side down on a clean dishtowel laid flat on the counter. Place the lids and rings in a saucepan and pour boiling water over them. Lift out with the sterilized tongs, and drain on a clean towel laid flat on the counter.
Put measured crushed berries in a pot. Add pectin and stir well. Place on high heat and stir constantly bringing quickly to a full boil with bubbles over the entire surface. Add sugar, continue stirring, and heat again to a full bubbling boil. Boil hard for 1 minute, stirring constantly. Remove from heat. Fill jars to 1/4 inch from top of jar. Wipe jam drips off jar mouth. Seal with the lid, tighten the ring, and turn the jar over on the towel until cool. Check to make sure that the lid is sealed by pressing on the center of the lid. If it pops back, the jar isn’t sealed and you’ll want to eat that one first.
Store in the refrigerator up to two months or for up to a year in the freezer.