When you come across dragonfruit puree (also labeled pitaya) in the freezer section, don't pass it up. It's the main component in this three-ingredient shrub, the one make most often, and it's how you get that alluring hot pink color. Shrubs are also known as drinking vinegars, and they can be a real bright spot in your refrigerator. A shrub like this one keeps for weeks, and a splash of it in soda water, Prosecco, or even a salad dressings is electric. A flexible bolt of sweet and sour.