Briefly rinse the elderflowers – they must have just blossomed. Cut the lemon into thin slices and put them with the flowers and the rest of the ingredients in a large container, stir.
Cover the jar and put it in a warm place. After 24 hours the elderberry juice is ready to drink. Repeatedly season with honey and lemon if necessary.
After 2-3 days the drink begins to mousse. Pour off the juice, fill it into bottles with screw tops and put them in a dark place. In about 4 weeks the juice has become sparkling wine.