Pluck the cleaned lilac blossoms from the stems. Wash the lemon, cut into slices and add to the flowers.
Dissolve the sugar in the water while stirring and allow to cool. Add the citric acid when the sugar water is still lukewarm. Pour over the blossom-lemon mixture and stir a little.
Cover and leave to stand in a cool place for 5 days and stir daily. Strain and fill into small bottles. Can only be kept in the refrigerator for approx. 4 weeks.
Depending on the color of the flowers, the syrup is also colored differently. Boiling and filling hot extends the shelf life, but the color then diminishes.