Step 1: Prepare the Berry Syrup. In a medium saucepan, combine mixed berries, granulated sugar, and 1 cup of water. Bring to a simmer over medium heat, stirring occasionally, until the sugar is dissolved and berries have softened (about 5-7 minutes).
Step 2: Blend the Syrup. Remove the berry mixture from heat and let it cool slightly. Transfer the mixture to a blender and blend until smooth. For a pulp-free slushie, strain the mixture through a fine-mesh sieve, pressing down on the solids to extract all liquid. Discard pulp.
Step 3: Combine with Liquids. In a large pitcher or directly in your slushie machine reservoir, combine the strained berry syrup (or un-strained, if you prefer some pulp), the remaining 3 cups of cold water, and the fresh lemon juice (and optional lime juice). Stir well to combine all ingredients.
Step 4: Freeze in Slushie Machine. Pour the liquid mixture into your slushie machine. Follow your machine’s specific instructions for operation. Typically, you’ll set it to the ‘slush’ or ‘freeze’ setting and allow it to churn for 20-30 minutes, or until it reaches the desired slushy consistency.
Step 5: Serve and Enjoy. Once the Berry Blast Slushie is ready, dispense into glasses. Garnish with fresh berries, a lemon or lime slice, or a sprig of mint for an extra touch. Enjoy immediately!