Combine the fresh strawberries, water, and sugar in a medium saucepan over medium heat. Stir the mixture gently until the sugar completely dissolves, about 3-4 minutes, and you see small bubbles forming around the edges of the pan.
Bring the strawberry mixture to a gentle boil, then reduce heat to low and simmer for 8-10 minutes until the strawberries are very soft and the liquid has turned a deep pink color. Use a wooden spoon to gently mash the strawberries against the side of the pan to release more flavor and color.
Remove the saucepan from heat and stir in the acai powder and green coffee extract if using, whisking thoroughly until no clumps remain and the mixture is smooth. The acai will deepen the color to a rich magenta hue that's characteristic of the Starbucks version.
Place a fine mesh strainer over a large pitcher and carefully pour the strawberry acai mixture through it, pressing down on the solids with the back of a spoon to extract all the flavorful liquid. Discard the strawberry pulp and allow the concentrate to cool to room temperature, then refrigerate until completely chilled, about 2 hours or overnight.
To assemble each refresher, fill a tall glass with ice cubes until it's about three-quarters full. Pour 1/4 cup of the chilled strawberry acai concentrate over the ice, watching as it cascades down through the cubes.
Add 3/4 cup of chilled white grape juice to each glass, stirring gently with a long spoon to combine the concentrate and juice. The drink should be a beautiful pink color with a slightly translucent quality.
Top each drink with a small handful of freeze-dried strawberries, which will float on top and gradually rehydrate, adding bursts of intense strawberry flavor. For the Pink Drink version, substitute 1/4 cup of coconut milk for some of the white grape juice for a creamy, tropical twist.
Serve immediately with a straw and enjoy your homemade Starbucks Strawberry Acai Refresher. Store any leftover strawberry acai concentrate in an airtight container in the refrigerator for up to one week, making it easy to whip up fresh drinks whenever the craving strikes.
