Pick fresh lilac clusters when in bloom. Approximately 4 clusters yield 1 cup of flowers, but this will also depend on the variety of lilacs, and the size of the clusters. Using a fine-mesh strainer, rinse the flowers thoroughly to remove any dust or tiny insects. Try to avoid adding the green stems and leaves, which some say can make the syrup bitter.
Add lilacs, sugar, orange slices, and cardamom (if using) to a small saucepan and cover with 1 cup of water. If you want to tint the syrup purple, add a few blueberries.
Stir to dissolve the sugar while bringing the mixture to a boil over medium heat. Continue to boil for 5 minutes, then turn off the heat and allow the lilacs to infuse the syrup for 4 to 8 hours.
Strain the syrup using a fine strainer. A soup bag would be even better. Press down on the flowers to extract as much syrup as possible.
Pour the Lilac Simple Syrup in a sterilized jar or bottle and keep it refrigerated.
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Notes
If you add blueberries to enhance the color of the syrup, cut them in half and smash them, if necessary, to release their color.
The longer you allow the syrup to infuse, the stronger the lilac flavor will be.
Do you have access to a lot of lilac bushes? If so, make larger batches of syrup and can use it when lilacs are not in season.
Make a thicker syrup and pour over pancakes or waffles.
Freeze lilac syrup in ice cube trays and plop the cubes into a jar of lemonade or iced tea. Go a step further and add a few lilacs into each cube before freezing.
Use it in cocktails and to flavor vodka and gin-based drinks.
When stored in the fridge, the lilac syrup should be good for a few months. Store in the freezer for longer storage.
A way to tell if the lilac syrup has gone bad is if the syrup at the bottom of the jar gets cloudy. If this happens, discard the syrup.