Blueberry jam can be used in many different ways. Wash and drain the blueberries and put them in a saucepan. Mix with gelling sugar and lemon juice and puree. Bring the blueberry jam to the boil. Skim off the foam. It tastes very delicious cold on rolls. Cook the blueberry jam for 3 minutes while stirring. Immediately fill into 3 jam jars. Pull the film through the rum to keep it fresh. Place on the opening of the glasses. Screw the cover tight. Place the glasses on the lid for 5 minutes. Turn around and allow to cool. The calories are calculated per glass. If you eat 20 g blueberry jam per serving, that's about 50 calories.