The drupes (fruit) of the genus Rhus are ground into a deep-red or purple powder and used as an acidulant in Middle Eastern cuisine to add a lemony taste to salads or meat; in Turkish cuisine e.g. added to salad-servings of kebabs and lahmacun. In North America, the smooth sumac (Rhus glabra), and the staghorn sumac (Rhus typhina), are sometimes used to make a beverage, termed "sumac-ade" or "Indian lemonade" or "rhus juice". This drink is made by soaking the drupes in cool water, rubbing them to extract the essence, straining the liquid through a cotton cloth and sweetening it.
Where can I buy sumac?
Until the supermarkets catch on to this one, then Greek, Turkish, Lebanese ethnic stores are the best places to buy sumac.