Prepare Jars: Examine all jars for cracks or chips and discard any damaged jars. Wash jars and rings in hot soapy water, rinse thoroughly, and keep jars hot in a 180°F oven or hot water until ready to fill.
Heat Lids: Place new canning lids in a small saucepan, cover with hot water at 180°F, and keep hot until ready to use. Do not boil lids as this may damage the sealing compound.
Prepare Canner: Fill your boiling water bath canner with enough water to cover jars by 1-2 inches when submerged. Begin heating water to a rolling boil while preparing jam.
Prepare Strawberries: Wash strawberries in cold water and remove hulls. Crush berries in batches using a potato masher, leaving some texture for chunky jam or crush completely for smooth jam. Measure exactly 5 cups of crushed berries.
Combine Fruit and Pectin: In a large heavy-bottomed pot, combine crushed strawberries with powdered pectin, stirring thoroughly until pectin is completely dissolved with no lumps remaining.
Boil Fruit Mixture: Add bottled lemon juice to strawberry mixture and bring to a full rolling boil over high heat, stirring constantly. The mixture must boil vigorously and cannot be stirred down.
Add Sugar: Add all 7 cups of sugar at once to the boiling strawberry mixture, stirring constantly to dissolve completely. Return to a full rolling boil and boil hard for exactly 1 minute, stirring constantly.
Test and Fill: Remove jam from heat and quickly skim off any foam with a metal spoon. Using a ladle and wide-mouth funnel, fill hot jars with jam, leaving exactly 1/4 inch headspace from the rim.
Remove Air and Seal: Remove air bubbles by running a plastic tool around the inside of each jar, adjusting headspace if necessary. Wipe jar rims thoroughly with a clean, damp paper towel and center hot lids on jars with rings finger-tight only.
