Wash the fruit and let it drip off. Remove the stalks and stones from cherries. Clean the strawberries. Strip currants from the stalks with a fork. Sort the raspberries. Weigh 1 kg of fruit. Mix with jam sugar in a large pot.
Cover and let the juice steep for 3-4 hours.
Bring the fruit to the boil over high heat while stirring. Then boil for at least 3 minutes while stirring constantly. Stir in lemon juice.
Pour hot jam into prepared twist-off jars. Seal immediately and let cool upside down.