Here is a very old recipe for Elderflower Vinegar:
Take 2 lb. of dried flowers of the European Elder. If you use your own flowers, pluck carefully their stalks from them and dry them carefully and thoroughly. This done, place in a large vessel and pour over them 2 pints of good vinegar. Close the vessel hermetically, keep it in a very warm place and shake them from time to time. After 8 days, strain the vinegar through a paper filter. Keep in well-stoppered bottles.
This is an old-world simple, but rarely met with nowadays, but worth the slight trouble of making. It was well-known and appreciated in former days and often mentioned in old books; Steele, in The Tatler, says: ‘They had dissented about the preference of Elder to Wine vinegar.’
From: A Modern Herbal