Day 1: Sort and rinse the blackberries without soaking them.
Do the same for the blueberries.
Quickly rinse the strawberries with clear water, dry them in a towel, top and tail them and cut them in half.
Sort the raspberries if necessary and avoid rinsing them to preserve their flavor.
Mix the strawberries, raspberries, blackberries, blueberries, sugar, and lemon juice in a large bowl.
Cover with parchment paper and let it marinate for 1 hour.
Pour this preparation into a jam pan or a large saucepan and bring to a simmer, stirring gently.
Pour this cooking into a bowl, cover with parchment paper and refrigerate overnight.

Day 2: Pour the preparation into the jam pan or a large saucepan and bring to a boil, stirring gently.
Maintain the cooking over high heat for about 5 to 10 minutes, stirring constantly.
Check the consistency of the jam by dropping a few drops onto a small cold plate: it should slightly gel.
Remove the pan from the heat and immediately put it in jars and cover.