Wash the umbels carefully and then put them in a large pan or bowl and pour 3 liters of water over them. Optionally, you can put a weight on the elderflowers to keep them submerged. Leave this covered with a plate, lid or cloth for 1 day at room temperature.
500 g elderflower blossom, 3 l water
Now strain the liquid through a sieve and, if you want it very nicely clear, through a clean cloth, then measure out the amount of water. Make up to 3 liters.
Meanwhile, sterilize your bottles and jars by filling them with boiling water.
Add sugar and lemon juice to the elderflower water. If you used more or less elderflower and water than the exact recipe, use the following rule of thumb: about 800 grams to 1 kg of sugar and the juice of half a lemon per liter of liquid. Want a less sweet but still a nice viscous syrup? Then use gelling sugar.
2400 g sugar, 2 lemons
Bring the water with sugar and lemon to a boil. Let boil for 3 minutes and then turn off the heat. Pour the hot elderflower syrup into the clean bottles or jars sterilized with boiling water and seal immediately with a lid. Let cool and store the syrup in a cool dark place.