Rinse fresh berries and pat dry; slice or quarter any large berries. If using frozen berries, no thawing is needed.

In a 1-quart glass jar with a lid, combine the prepared berries and granulated sugar. Stir gently to coat the berries evenly.

Cover the jar and let the mixture sit at room temperature for 24 to 48 hours, stirring occasionally, until the sugar has dissolved and the berries have released their juices.

Pour the vinegar into the jar with the berry-sugar mixture and stir well to combine.

Cover the jar and refrigerate for another 24 hours to allow the flavors to meld and infuse.

Place a fine-mesh sieve over a clean bowl or pitcher. If desired, line the sieve with cheesecloth for a clearer shrub.

Pour the shrub mixture into the sieve and allow it to drain completely, without pressing on the solids, until all the liquid is collected.

Discard the berry solids. Transfer the finished shrub concentrate to a clean, airtight bottle or jar and store it in the refrigerator.

To serve, mix 1 to 2 tablespoons of shrub concentrate with 6 to 8 ounces of cold club soda or sparkling water over ice.

Garnish with fresh berries or a sprig of your favorite herb, such as mint or basil, if desired.