Makes 4 pints of jam
Prepare jars and lids and bands by washing in hot water. Let lids stand in hot water until ready to use.
4 pints strawberries, discard stems and crush with potato masher to make 4 cups of crushed berries.
Use this exact amount of berries with exactly 7 cups of sugar and ½ teaspoon of butter (to reduce foaming). Stir together in 6 or 8 quart saucepot, bring to full rolling boil, that doesn’t stop bubbling when stirred, on high heat, stirring constantly.
Stir in 1 pouch Certo liquid pectin and return to full rolling boil and boil exactly 1 minute, stirring constantly.
Remove from heat.
Ladle quickly into prepared jars, filling to within 1.8 inch. Wipe jar rims and threads, cover with two-piece lids, screw bands tightly. Place jars on elevated rack in canner, water must cover jars by 1 to 2 inches, add more boiling water if necessary. Cover, bring to gentle boil, process jam 10 minutes. Remove jars and place on towel to cool. After jars cool, check seals by pressing on middle of lid with finger. If lid springs back, lid is not sealed and refrigeration is necessary.