Shake any bugs loose from the elderflower, then strip the florets from the heads with a fork. Let the sugar water cool to 20C and stir in the lemon zest, juice, flowers and yeast. Cover, and leave to ferment out of direct sunlight for six days. If your bucket doesn't have an airlock lid, gently rest the lid on top of the bucket.
Strain through boiled or sanitised muslin into the second sanitised bucket, leaving the sediment behind. Leave it to sit for a couple of hours for any last pollen or sediment to settle.
Siphon into sanitised wine or fizzy drink bottles and seal. Leave for five days in a cool dark place. Check the carbonation by lightly opening the lids to vent excess CO2. Keep in fridge if notably vigorous.
If you drop the sugar to 1.6kg, it shouldn’t finish above 8% abv, at 2kg, 10%. Champagne yeast is tolerant up to at least 15%.
Use the elderflower straight awayElderflower wilts very fast, so aim to make this champagne as soon as you return from picking them.