Place 6 clean 250 ml mason jars on a rack in a boiling water canner; cover jars with water and heat to a simmer (180°F/82°C). Set screw bands aside. Heat SNAP LID® in hot water, not boiling (180°F/82°C). Keep jars and lids hot until ready to use.
Wash, hull and crush strawberries, one layer at a time. Measure 3 cups (750 ml). Measure sugar; set aside.
In a large deep stainless steel saucepan, combine prepared strawberries, pineapple, 1/2 tsp (2 ml) butter or margarine to reduce foaming, and Bernardin Original Pectin, stirring until pectin is dissolved. Over high heat, bring mixture to a full rolling boil. Add all of the sugar. Stirring constantly, return mixture to a full rolling boil that cannot be stirred down. Boil hard 1 minute, stirring constantly. Remove from heat; skim off foam, if necessary.
Quickly ladle jam into a hot jar to within 1/4 inch (0.5 cm) of top of jar (headspace). Using nonmetallic utensil, remove air bubbles and adjust headspace, if required, by adding more fruit mixture. Wipe jar rim removing any food residue. Centre hot sealing disc on clean jar rim. Screw band down until resistance is met, then increase to fingertip tight. Return filled jar to rack in canner. Repeat for remaining fruit mixture.
When canner is filled, ensure that all jars are covered by at least one inch (2.5 cm) of water. Cover canner and bring water to full rolling boil before starting to count processing time. At altitudes up to 1000 ft (305 m), process –boil filled jars – 10 minutes.*
When processing time is complete, remove canner lid, wait 5 minutes, then remove jars without tilting and place them upright on a protected work surface. Cool upright, undisturbed 24 hours; DO NOT RETIGHTEN screw bands.
After cooling check jar seals. Sealed lids curve downward and do not move when pressed. Remove screw bands; wipe and dry bands and jars. Store screw bands separately or replace loosely on jars, as desired. Label and store jars in a cool, dark place. For best quality, use home canned foods within one year.