For one cup of grenadine, bring 3 cups of pomegranate juice (see above) to a boil over medium-high heat, then simmer uncovered until reduced to one cup, about an hour, stirring and skimming the froth now and then. Cool and store in the refrigerator.
The store-bought grenadine of my childhood Shirley Temple days is mostly sugar and red dye. This recipe produces slightly sweet pomegranate juice concentrate that isn’t cloying. For Shirley Temples, fill a glass with ginger ale, add a splash of grenadine, a twist of orange or lemon, and don’t forget the cherry! For a boy’s Rob Roy, fill a glass with cola, add a splash of grenadine, add a twist of lemon and a cherry. So sophisticated!