01 - Combine strawberries, rhubarb, raspberries, and mixed berries in a large non-reactive pot. Mash lightly with a potato masher to release natural juices, creating a chunky fruit base.
02 - Stir in lemon juice and fruit pectin until well distributed. Let the mixture stand for 5 minutes to allow the pectin to activate.
03 - Place the pot over medium-high heat. Bring the fruit mixture to a boil, stirring frequently to prevent sticking and ensure even heating.
04 - Pour all the sugar into the pot at once. Stir continuously until completely dissolved. Return the mixture to a full, rolling boil and maintain for 1-2 minutes to reach setting point.
05 - Remove from heat immediately. Skim off any foam that has formed on the surface using a metal spoon for a cleaner appearance.
06 - Carefully ladle hot jam into sterilized jars, leaving ¼-inch headspace. Wipe rims clean, seal with lids, and process in a boiling water bath for 10 minutes for long-term storage. For immediate consumption, skip water bath and refrigerate.
07 - Allow jars to cool completely at room temperature. Check seals before storing. Refrigerate after opening and consume within 3 weeks for optimal freshness.