5poundseedless watermelonpeeled and cut into large chunks
5mint leavesplus more for garnish
24ounces (2 litres)seltzer water(see notes for substitutes)
ice to serve
Extract the Watermelon Juice
Put the watermelon chunks and mint leaves into your blender. Blend the watermelon and mint for 30 seconds-1 minute, or until no large chunks remain.
Once the watermelon is pureed, pour it mixture through a fine-mesh sieve that's been placed over a bowl. Use a rubber spatula to gently nudge the juice from the pulp through the sieve. You don't want a lot of watermelon flesh in the drink, so try not to press the flesh too hard.
Discard the watermelon pulp after you've extracted the juice. The extracted watermelon juice should measure approximately 6 cups.
Prepare the Watermelon Simple Syrup
In a pot, stir the watermelon juice and granulated sugar together. Bring this mixture up to a boil over medium heat, stirring frequently.
After the syrup comes to a boil and the sugar has dissolved, let it continue cooking for 30 seconds. Remove the syrup from the stovetop and set it on the countertop to cool completely.
When the watermelon simple syrup has cooled to room temperature, transfer it to a pitcher and put it into the fridge. Chill the simple syrup until very cold. Alternatively, you can set the pitcher in a bowl of ice water, to cool it down faster. Stir the syrup frequently and you can use it as soon as it is ice cold.
For a lightly sweetened soda: fill the glass 1/3 to 1/2 full with watermelon syrup. For a sweeter watermelon Italian soda: fill the glass 5/8s of the way with watermelon syrup.
Pour the seltzer water on top of the syrup filling the glass.Use a cocktail stirrer, or a straw, to stir the soda. Begin down at the bottom of the glass, and pull the syrup up while stirring into the seltzer to create a balanced drink.
Garnish each glass with a long stem of mint and a straw for sipping. Floaty bits of watermelon in the soda are to be expected since it's made with fresh juice.
Seltzer Substitutions: sparkling mineral water, club soda, tonic water, or sugar free ginger beer.Because the seltzer will go flat after a while, store the watermelon simple syrup in the fridge and make your Italian sodas "to order". For party Watermelon Italian Sodas, set up a watermelon Italian soda bar and let them create their own glass. Keep your watermelon simple syrup in a covered pitcher in the fridge for up to three days.