In a medium bowl, add berries and sugar and stir until well combined. Cover bowl tightly with plastic wrap and refrigerate until juice exudes from fruits and starts to combine with sugar to form a syrup, about 24 hours.
Strain fruit mixture through a fine-mesh strainer set over a medium bowl, pressing lightly on solids to express any remaining juice. Scrape any undissolved sugar into bowl with syrup. Whisk in vinegar.
Transfer syrup to a clean bottle. Close bottle, label with date, and shake vigorously. Refrigerate, shaking bottle periodically until sugar is completely dissolved, about 1 week. The shrub can be refrigerated for up to 1 year; the acid and sugar preserves the syrup and keeps it tasting bright and fresh.
