For the elderberry juice, wash elderberries, cut thick stems into small pieces. Heat the berries with lemon zest and water in a closed pot and boil until the berries burst open. Then let stand for half an hour.
Strain the juice through a cloth.
Mix the strained juice with sugar and boil for 2-3 min.
Sterilize bottles with hot water and pour the hot elderberry juice into the (preheated) bottles and close them quickly.