Now's the time to make your delicious fragrant Elderflower Cordial, capturing the taste of summer. You must pick the elderflowers on a dry, warm and sunny day, when the flower heads are fully open.  They must be perfect, with no trace of brown blossoms or squatters. Do not wash them so make sure that you pick them from an area where they are unikely to have been contaminated by wildlife or passing vehicles.The cordial will keep for several weeks in a cool pantry, several months in the fridge or alternatively freeze in plastic containers and it will keep for a year. Citric acid is available from chemists and DIY wine making suppliers, also worth looking in Middle Eastern shops.