If you are lucky enough to have a tree or know where to pick elderflowers give this a try. Pick flowers right after dew is dry from them and before the heat of day removes the fragrance. Morning is when they're at their most fragrant, Any of the top layer of flowers will oxidize from contact with air, turning brown. It's fine you can leave it be or place a weight on them to keep submerged, Do expect the liqueur to darken as it ages into a deep amber. This is OK.