Bring mixture to a boil, stirring constantly so you don't burn the sugar. After the boil let it simmer for 15 minutes.
Let the mixture cool to the point of not burning yourself when you work with it. Place the sieve over the bowl and pour the mixture into the sieve. Using a spatula mash the mixture until no more juice comes out. Be sure to scrape the underside of the sieve. A lot of juice will collect there.
Pour 2/3 cup of syrup into 2 bags. Label them. Lay flat in the freezer.
Put the blueberry syrup discard into the third bag to freeze. This can be used in quick bread, added to pancake batter, homemade ice cream or smoothies.