Pomegranate molasses
Pomegranate juice boiled down to a dark, thick syrup, sharply sour with a tart, fruity sweetness.
Pomegranate molasses is juice from mostly sour pomegranates, cooked down for a long time until it becomes an almost black, viscous syrup; in Persian cooking it is called rob-e anar, in Turkish nar ekşisi. Despite the name it is above all sour, with a deep, slightly astringent fruitiness and only restrained sweetness, and it is used more like vinegar or lemon to add acidity than like a syrup to sweeten. It gives stews, marinades, dressings and dips sourness, colour and a slight gloss. Products vary considerably: some are pure reduced juice, others are sweetened with sugar or adjusted with citric acid, which the ingredient list will show. It is sold in Turkish, Persian or Arab grocers, increasingly in well-stocked supermarkets, and by mail order; once opened it keeps a long time in the fridge.
Substitute:
The closest substitute is unsweetened pomegranate juice reduced to about a quarter and seasoned with lemon juice and a little sugar; this captures the fruit and acidity but usually ends up thinner and less deep. Balsamic vinegar with a little lemon juice replaces only the sourness and dark colour, bringing its own winey flavour and no taste of pomegranate.