Shrubs, also called drinking vinegars, are restorative drinks from the Colonial days predating soda pops and sports drinks. Prior to the invention of refrigeration, a shrub syrup was a means of preserving fruit long past its picking. Shrubs were popular in Colonial America, mixed with cool water to provide a pick-me-up on hot summer days. A proper shrub has a flavor that's both tart and sweet, so it stimulates the appetite while quenching thirst. Try your rhubarb shrub over ice with club soda. Steeping time not included in preparation time.