How to make
Clean and wash the blackberries. Sprinkle them with sugar and leave them overnight.
Put the pot on high heat. Once it boils, reduce the heat and boil the jam to the desired thickness (a drop on a plate, shouldn't be runny).
Stir and skim off the foam that forms. Finally, add the citric acid.
After 5 minutes, remove from the heat and fill the warmed jars with jam. Close and turn the lids facing down.
Leave them to cool and store them in a cool place. To be safe, you can boil the jars for 5 minutes.
Grandma's blackberry jam is ready.
