Wash the cherries thoroughly and remove the pits, use a special machine or needle for this.
Pour the sugar in the water and boil until the syrup thickens.
Remove from the heat and put the fruit in. Allow the fruit to take in some of the syrup. Return to the heat. Boil to thicken the syrup again.
Five minutes before removing from the heat, add the citric acid. Put vanilla in at the last minute.
Pour it into jars and close while hot. Turn them with their caps down, to create a vacuum.