Run the blueberry mixture through a fine-mesh sieve set over a bowl or container. Using the back of a wooden spoon, mash the mixture against the sieve to ensure you get all the syrup. Discard the leftover contents in the sieve. Let the syrup cool to room temperature and chill in the refrigerator before using.
For the blueberry soda: Fill a 16-ounce glass halfway with ice, add 1/4 cup blueberry syrup, top with seltzer and stir gently to combine.
The recipe makes approximately 4 cups of syrup. The syrup will last up to 2 weeks covered and refrigerated.
This recipe was provided by professional chefs and has been scaled down from a bulk recipe provided by a restaurant. The Food Network Kitchens chefs have not tested this recipe, in the proportions indicated, and therefore, we cannot make any representation as to the results.