Shrubs are drinks that date back to Colonial days when they were made with sweetened vinegar fruit syrups blended with rum or brandy. Nowadays, a shrub typically consists of the syrup stirred into a glass of flat or sparkling ice water.
1. Combine cider vinegar, sugar, and ginger in large pot, and bring to a boil. Add rhubarb, reduce heat to medium-low, and simmer 5 to 7 minutes, or until rhubarb is tender and falling apart, stirring occasionally. Cool, then chill. 2. Line sieve with cheesecloth, and place over large bowl. Pour rhubarb mixture into sieve, and let drain, pressing to extract all liquid. Reserve solids for another use. (They can be turned into chutney.) Transfer syrup to covered jar, and refrigerate until ready to use. 3. To serve: Pour 4 to 5 Tbs. syrup in bottom of glass with ice. Top with 6 oz. seltzer or ice water. Garnish each glass with mint sprig, if using.